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OChem1 Practice Exams
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Dr. Peter Norris, 2014
Chemistry 3719
Practice Exam A1
This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam and you may use molecular models as needed. Good Luck.
1. (8 pts) Draw structures for all of the cycloalkane isomers with the formula C5H10, and then give each of your
structures an acceptable name. (Klein Chapter 4)
1
2. (9 pts) Give each of the following organic molecules an acceptable name. You may use either systematic or
common names for substituents. (Klein Chapter 4)
CH3
a.
CH2CH3
b.
c.
3. (8 pts) Fill in the ground state electron distribution for O (from the periodic table), and then construct hybrid
orbital pictures for the highlighted O atoms that describe the orbitals used for bonding in each case. (Klein
Chapter 1)
Explain briefly why hybrid orbitals are necessary here:
2
4. (12 pts) Give the products expected from each of the following acid-base reactions. Then label each acid
with an approximate pKa and indicate whether products, reactants, or neither are favoured in each case.
(Klein Chapter 3)
CO2H
a.
+ CH3CH2OK
C
b.
C
+
H
LiN[CH(CH3)2]
OH
c.
+ CH3ONa
5. (8 pts) Give the three acids below an approximate pKa value and then explain why they have such different
acid strengths even though they each have an OH group as the acidic component. (Klein Chapter 3)
3
6. (6 pts) Complete the following structures by adding any needed formal charges. (Klein Chapter 2)
7. (6 pts) Draw a second resonance structure and an overall hybrid for each of the following species. (Klein
Chapter 2)
O
a.
H3C
b.
O
H
C
N
N
H
CH3
c.
O
CH2
8. (6 pts) For the three molecules below, discuss their relative solubilities in aqueous solution in terms of the
forces that are playing a role here. (Klein Chapter 1)
4
9. (10 pts) Draw two chair conformations for cis-1-t-butyl-3-methylcyclohexane that are related through a
ring-flip. Then circle which conformation you expect to be more stable and explain why. Then do the same
for the trans isomer and, finally, indicate whether the cis or trans isomer should be more stable overall and
explain your choice. (Klein Chapter 4)
10. (9 pts) Draw Newman depictions that correspond to the following conformations. (Klein Chapter 4)
a. The least stable conformation of 3-methylnonane along the C-4–C-5 bond.
b. The most stable conformation of 1,1-dibromo-6-chlorohexane along the C-3–C-4 bond.
c. A gauche conformation for 5-methyl-2-heptanol along the C-3–C-4 bond.
5
11. (9 pts) Rank the following species as indicated: (Klein Chapters 1-3)
a. Lowest to highest electronegativity (1 = lowest, 5 = highest)
b. Lowest to highest pKa (1 = lowest, 5 = highest)
c. Lowest to highest boiling point (1 = lowest, 5 = highest)
12. (9 pts) Within each pair of molecules below, indicate which is more stable and then give a brief explanation
for your choices in each case. (Klein Chapters 3-4)
ONa
ONa
a.
vs.
Br
Br
Br
b.
OLi
c.
Br
vs.
NHLi
vs.
6
Chemistry 3719
Practice Exam A1 Key
This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam and you may use molecular models as needed. Good Luck.
1. (8 pts) Draw structures for all of the cycloalkane isomers with the formula C5H10, and then give each of your
structures an acceptable name. (Klein, Chapter 4)
1
2. (9 pts) Give each of the following organic molecules an acceptable name. You may use either systematic or
common names for substituents. (Klein Chapter 4)
CH3
a.
5-ethyl-1-isopropyl-2-methyl-3-propylcyclohexane
CH2CH3
b.
5-isopropyl-2,6,7-trimethylnonane
c.
bicyclo[4.3.1]decane
3. (8 pts) Fill in the ground state electron distribution for O (from the periodic table), and then construct hybrid
orbital pictures for the highlighted O atoms that describe the orbitals used for bonding in each case. (Klein
Chapter 1)
Explain briefly why hybrid orbitals are necessary here:
The most obvious reason is that the lone pairs in the ground state structure of Oxygen are not equivalent; the
hybridization model fixes that.
2
4. (12 pts) Give the products expected from each of the following acid-base reactions. Then label each acid
with an approximate pKa and indicate whether products, reactants, or neither are favoured in each case.
(Klein Chapter 3)
CO2H
a.
CO2K
+ CH3CH2OK
products f avoured
pKa ~ 5
C
b.
+ CH3CH2OH
C
+
H
C
LiN[CH(CH3)2]
pKa ~ 26
Li
HN[CH(CH3)2]
pKa ~ 38
products f avoured
ONa
+ CH3ONa
pKa ~ 16
C
+
OH
c.
pKa ~ 16
+ CH3OH
neither f avoured
pKa ~ 16
5. (8 pts) Give the three acids below an approximate pKa value and then explain why they have such different
acid strengths even though they each have an OH group as the acidic component. (Klein Chapter 3)
The first molecule has pKa = 16 since it is an alcohol, the second has pKa ~5 since it is a
carboxylic acid, and the third has pKa = 10 since it is a phenol. The difference in pKa values is
down to the relative stabilities of the conjugate bases formed from each; the first compound
produces an anion in which the charge is localized on O and therefore unstable. The carboxylic
acid produces a conjugate base in which the charge is delocalized onto two O atoms, which is
quite stable. The third molecule also has a resonance-stabilized conjugate base, however here the
charge is delocalized into O and C, which isn’t as favourable as the carboxylate situation. The
more stable the conjugate base, the more acidic the associated acid.
3
6. (6 pts) Complete the following structures by adding any needed formal charges. (Klein Chapter 2)
7. (6 pts) Draw a second resonance structure and an overall hybrid for each of the following species. (Klein
Chapter 2)
8. (6 pts) For the three molecules below, discuss their relative solubilities in aqueous solution in terms of the
forces that are playing a role here. (Klein Chapter 1)
Molecule A will be the least soluble in water since although features a hydrogen-bonding
alcohol it also has a hyprophobic alkyl chain that will repel water. Molecule B has a
shorter alkyl chain so the OH group will have more of a role than in A and increase water
solubility. Molecule C should be the most soluble since it is ionic.
4
9. (10 pts) Draw two chair conformations for cis-1-t-butyl-3-methylcyclohexane that are related through a
ring-flip. Then circle which conformation you expect to be more stable and explain why. Then do the same
for the trans isomer and, finally, indicate whether the cis or trans isomer should be more stable overall and
explain your choice. (Klein Chapter 4)
10. (9 pts) Draw Newman depictions that correspond to the following conformations. (Klein Chapter 4)
a. The least stable conformation of 3-methylnonane along the C-4–C-5 bond.
b. The most stable conformation of 1,1-dibromo-6-chlorohexane along the C-3–C-4 bond.
c. A gauche conformation for 5-methyl-2-heptanol along the C-3–C-4 bond.
5
11. (9 pts) Rank the following species as indicated: (Klein Chapters 1-3)
a. Lowest to highest electronegativity (1 = lowest, 5 = highest)
3
5
4
1
2
3
5
2
5
b. Lowest to highest pKa (1 = lowest, 5 = highest)
2
4
1
c. Lowest to highest boiling point (1 = lowest, 5 = highest)
3
1
4
12. (9 pts) Within each pair of molecules below, indicate which is more stable and then give a brief explanation
for your choices in each case. (Klein Chapters 3-4)
6
Chemistry 3719
Practice Exam A2
This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam and you may use molecular models as needed. Good Luck.
1. (9 pts) For each of the following pairs of molecules, provide the configuration of each chiral centre and then
indicate whether the two molecules within a pair are enantiomers, diastereomers, or are identical. (Klein
Chapter 5)
OH
a.
and
Br
O
CH3
H
Br
H
OH
CH3
CH3
CH3
and
b.
O
CH3
c.
H
CH2Cl
OH
H
F
CH3
CH3
OH
and
CH2Cl
H3C
F
1
2. (9 pts) Give each of the following organic molecules an acceptable name. You may use either systematic or
common names for substituents. (Klein Chapters 7-8)
a.
Br
OH
F F
b.
OH
c.
I
Cl
3. (8 pts) Provide a detailed mechanism for the following transformation that uses curved arrows to show the
breaking and forming of bonds. Explain why this product is the major product formed. (Klein Chapter 8)
2
4. (8 pts) The following solvolysis conditions give two major products in equal amounts but, when measured
for the mixture, [α]D ≠ 0. Provide the products and a mechanism for this process, as well as an explanation
for the optical rotation data. (Klein Chapter 7)
5. (8 pts) The following reactions have only slight differences; however the ratio of products formed in each
case is dramatically different. Provide a detailed mechanistic explanation for this data. (Klein Chapter 8)
6. (6 pts) Rank the following in decreasing order of reaction rate in SN1 with HBr (4 = fastest, 1 = slowest) and
then give a brief explanation for your choices. (Klein Chapter 7)
3
7. (10 pts) On the axes given below, draw a complete reaction profile for the following reaction that includes
diagrams of all intermediates and transition states involved. (Klein Chapters 6-7)
NaCl
Cl
Br
P.E.
reaction coordinate
8. (8 pts) Give the major products expected from each step in the following synthetic sequence. Be careful to
take into account any stereochemical issues along the way. (Klein Chapter 7)
4
9. (15 pts) Give the expected products, major and minor where applicable, in each of the following situations.
Be sure to take into account any changes in stereochemistry that may occur. (Klein Chapters 7-8)
OH
H3C
1.
a.
SO2Cl
pyridine
2. NaCN, DMF
H
b.
OH
H2SO4, heat
O
I
c.
CH3OH
O
H
Br
d.
e.
CH2OH
H
I
H
OH
CH3
NaOCH3, DMF
NaN3, DMSO
5
10. (8 pts) Give a mechanism for the following reaction using curved arrows to describe all bond-forming and
breaking events. Then draw a transition state for the R.D.S. and explain why this is the major product.
(Klein Chapter 8)
11. (6 pts) Convert the following stereochemical representations as directed. Working out R/S configurations
might help but are not required as part of the answer. (Klein Chapter 5)
12. (5 pts) Dehydration of a tertiary alcohol in the presence of catalytic acid through the E1 pathway is thermodynamically unfavourable since sigma bonds are swapped for a pi bond. Explain how this process is made
viable such that the alkene is able to be formed and isolated in high yield. (Klein Chapter 8)
6
Chemistry 3719
Practice Exam A2 Key
This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam and you may use molecular models as needed. Good Luck.
1. (9 pts) For each of the following pairs of molecules, provide the configuration of each chiral centre and then
indicate whether the two molecules within a pair are enantiomers, diastereomers, or are identical. (Klein
Chapter 5)
1
2. (9 pts) Give each of the following organic molecules an acceptable name. You may use either systematic or
common names for substituents. (Klein Chapters 7-8)
3. (8 pts) Provide a detailed mechanism for the following transformation that uses curved arrows to show the
breaking and forming of bonds. Explain why this product is the major product formed. (Klein Chapter 8)
The secondary carbocation that is formed undergoes rearrangement to produce a better tertiary cation that
no longer has the strained cyclobutyl ring involved. The tertiary carbocation is then deprotonated to give
the most highly substituted alkene which is stabilized by four electron-donating alkyl groups through
inductive effects.
2
4. (8 pts) The following solvolysis conditions give two major products in equal amounts but, when measured
for the mixture, [α]D ≠ 0. Provide the products and a mechanism for this process, as well as an explanation
for the optical rotation data. (Klein Chapter 7)
5. (8 pts) The following reactions have only slight differences; however the ratio of products formed in each
case is dramatically different. Provide a detailed mechanistic explanation for this data. (Klein Chapter 8)
6.
(6 pts) Rank the following in decreasing order of reaction rate in SN1 with HBr (4 = fastest, 1 = slowest)
and then give a brief explanation for your choices.
The better the possible carbocation, the faster the SN1 reaction; 3° > 2° > 1° > CH3
3
7. (10 pts) On the axes given below, draw a complete reaction profile for the following reaction that includes
diagrams of all intermediates and transition states involved. (Klein Chapter 7)
NaCl
Cl
Br
P.E.
A
B
‡
A=
+
C
-
Br
‡
B=
+
+
H
C=
‡
+
Cl -
Br
Cl
reaction coordinate
8. (8 pts) Give the major products expected from each step in the following synthetic sequence. Be careful to
take into account any stereochemical issues along the way. (Klein Chapter 7)
4
9. (15 pts) Give the expected products, major and minor where applicable, in each of the following situations.
Be sure to take into account any changes in stereochemistry that may occur. (Klein Chapters 7-8)
OH
H3C
1.
a.
SO2Cl
pyridine
OTs
CN
1.
2.
2. NaCN, DMF
SN2 - inversion
H
b.
OH
H2SO4, heat
O
O
E1 - Zaitsev outcome
I
c.
OCH3
OCH3
CH3OH
+
O
O
O
SN1 - racemic
H
Br
d.
NaOCH3, DMF
1.
OCH3
H
2.
SN2 - inversion
e.
CH2OH
H
I
H
OH
CH3
CH2OH
N3
H
H
OH
CH3
NaN3, DMSO
SN2 - inversion
5
E2
10. (8 pts) Give a mechanism for the following reaction using curved arrows to describe all bond-forming and
breaking events. Then draw a transition state for the R.D.S. and explain why this is the major product.
(Klein Chapter 8)
Br
NaOCH2CH3
H
OCH2CH3
E2
Br -
‡
H
- OCH2CH3
The major product is the most highly-substituted and stabilized alkene (tetrasubstituted)
11. (6 pts) (6 pts) Convert the following stereochemical representations as directed. Working out R/S
configurations might help but are not required as part of the answer. (Klein Chapter 5)
12. (5 pts) Dehydration of a tertiary alcohol in the presence of catalytic acid through the E1 pathway is thermodynamically unfavourable since sigma bonds are swapped for a pi bond. Explain how this process is made
viable such that the alkene is able to be formed and isolated in high yield. (Klein Chapter 8)
Run the reaction at high temperature to increase the contribution of entropy to the overall free energy of
the system (∆G = ∆H – T∆S) since the reaction is entropically favoured (1 mole of alcohol produces two
moles of product; alkene and water). High temperature also allows the more volatile alkene to be removed
by distillation which will then force the equilibrium towards product to compensate.
6
Chemistry 3719
Practice Exam A3
This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam and you may use molecular models as needed. Good Luck.
1. (9 pts) Within each of the following pairs of molecules, indicate which will react at a faster rate in the given
reaction; then give a brief explanation for your choice in each case. (Klein Chapters 7-9)
CH3
a.
CH3
or
H3C
in electrophilic addition
H
H H
D D
b.
Br
or
Br
in E2 elimination
c.
OH
or
OH
in SN2 substitution
1
2. (9 pts) Give each of the following organic molecules an acceptable name using any systematic or common
names for substituents where appropriate. Be sure to include stereochemical designators where needed.
(Klein Chapteres 5-10)
OH
a.
F
Br
Cl
b.
F
c.
HO
CH3
3. (9 pts) For the following conversion, provide a detailed mechanism for the first operation only (i.e. reaction
of the alkene with O3) that uses curved arrows to show the breaking and forming of bonds. (Klein Chapter
9)
2
4. (15 pts) Give the ultimate major product expected in each of the following situations. (Klein Chapters 9-11)
1. O3
a.
2. Zn, H2O
Br2, heat
b.
CH3CO3H
c.
Br2 in H2O
d.
CH3
H2, Pd
e.
CH3
3
5. (9 pts) Provide the major product expected under the following reaction conditions, and then give a detailed
mechanism (using curved arrows) that describes its formation. (Klein Chapter 10)
6. (9 pts) Show the major product expected under the following reaction conditions, name that product, and
then give a detailed mechanism (using curved arrows) that describes its formation. (Klein Chapter 11)
4
7. (8 pts) The following conditions induce a free radical halogenation process at the allylic position with only
two products forming with a combined [α]D = 0; give a mechanistic explanation for this observation. (Klein
Chapter 11)
8. (8 pts) Provide the major product expected under the following conditions and then a detailed mechanism
for its formation that includes all steps that lead to this product. (Klein Chapter 11)
9. (6 pts) Provide the reagents required to complete the following transformations. (Klein Chapter 9)
5
10. (8 pts) The following hydroboration-oxidation sequence results in the alkylborane and alcohol shown below.
Explain how the regiochemical and stereochemical outcomes help determine the mechanism in each step.
(Klein Chapter 9)
11. (10 pts) On the axes given below, draw a complete reaction profile for the following reaction that includes
diagrams of all intermediates and transition states involved. (Klein Chapter 9)
HBr
Br
P.E.
reaction coordinate
6
Chemistry 3719
Practice Exam A3 Key
This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam and you may use molecular models as needed. Good Luck.
1. (9 pts) Within each of the following pairs of molecules, indicate which will react at a faster rate in the given
reaction; then give a brief explanation for your choice in each case. (Klein Chapters 7-9)
1
2. (9 pts) Give each of the following organic molecules an acceptable name using any systematic or common
names for substituents where appropriate. Be sure to include stereochemical designators where needed.
(Klein Chapteres 5-10)
OH
a.
(3R,6S)-6-fluoro-7-methyloct-4-yn-3-ol
F
Br
Cl
b.
(R,Z)-2-bromo-5-chloro-6-methylhept-2-ene
F
c.
(1S,3R)-3-fluoro-5-methylcyclohept-4-enol
HO
CH3
3. (9 pts) For the following conversion, provide a detailed mechanism for the first operation only (i.e. reaction
of the alkene with O3) that uses curved arrows to show the breaking and forming of bonds. (Klein Chapter
9)
2
4. (15 pts) Give the ultimate major product expected in each of the following situations. (Klein Chapters 9-11)
H
1. O3
a.
O
O
2. Zn, H2O
H
Br
Br2, heat
b.
CH3CO3H
c.
O
Br
Br2 in H2O
d.
OH
CH3
e.
H CH
3
H2, Pd
CH3
CH3
H
3
5. (9 pts) Provide the major product expected under the following reaction conditions, and then give a detailed
mechanism (using curved arrows) that describes its formation. (Klein Chapter 10)
6. (9 pts) Show the major product expected under the following reaction conditions, name that product, and
then give a detailed mechanism (using curved arrows) that describes its formation. (Klein Chapter 11)
4
7. (8 pts) The following conditions induce a free radical halogenation process at the allylic position with only
two products forming with a combined [α]D = 0; give a mechanistic explanation for this observation. (Klein
Chapter 11)
8. (8 pts) Provide the major product expected under the following conditions and then a detailed mechanism
for its formation that includes all steps that lead to this product. (Klein Chapter 11)
9. (6 pts) Provide the reagents required to complete the following transformations. (Klein Chapter 9)
5
10. (8 pts) The following hydroboration-oxidation sequence results in the alkylborane and alcohol shown below.
Explain how the regiochemical and stereochemical outcomes help determine the mechanism in each step.
(Klein Chapter 9)
The first step involves regioselective addition of the borane reagent such that the larger substituent
on the alkene avoids the large bicyclic framework on boron; the oxidation step results in
stereochemical retention, which is only possible with a concerted migration step.
11. (10 pts) On the axes given below, draw a complete reaction profile for the following reaction that includes
diagrams of all intermediates and transition states involved. (Klein Chapter 9)
HBr
Br
P.E.
A
B
‡
A=
C
H Br
+
‡
B=
+
+
H
C=
‡
+
Br -
Br
reaction coordinate
6
Chemistry 3719
Practice Exam B1
This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam and you may use molecular models as needed. Good Luck.
1. (8 pts) Fill in the ground state electron distribution for N (from the periodic table), then construct hybrid
orbital pictures for the highlighted N atoms that describe the orbitals used by N for bonding in each case.
(Klein Chapter 1)
1
2. (20 pts) For each of the following acid-base reactions, draw the conjugate acid and conjugate base that are
expected to be formed. Label the acids on each side of the equations with approximate pKa values, and
indicate in each case if you expect the reaction to favour the left-hand side, the right-hand side, or neither.
(Klein Chapter 3)
OH
a)
+
NaOH
b)
CF3CH2OK
c)
d)
e)
+
CH3CH2OH
H
N
KNH2
+
NLi
+
C
C
OLi
H
OH
+
O
2
3. (15 pts) Provide acceptable names for the following molecules. Trivial or IUPAC names may be used as
appropriate. (Klein Chapter 4)
a)
CH3
H
CH2CH3
H3 C
H
CH3
b)
H
CH2CH(CH3)2
H
c)
d)
e)
3
4. (6 pts) Draw all of the isomeric alkanes that have the molecular formula C5H12 and give each of them a
suitable name. (Klein Chapter 4)
5. (6 pts) Provide any missing formal charges that are necessary in the following molecules. (Klein Chapter
1)
a.
b.
c.
6. (9 pts) Draw a second resonance structure for each of the following and indicate which structure you expect
to be more significant in each system. Be sure to put lone pairs in the correct places. (Klein Chapter 2)
O
a.
H3C
NH
OH
b.
O
c.
S
CH3
4
7. (10 pts) For cis-1-t-butyl-2-methylcyclohexane and trans-1-t-butyl-2-methylcyclohexane, draw two ringflipped chair forms for each isomer, then indicate the preferred conformation for each of the two isomers,
and finally indicate which if the two isomers is more stable. Explain your choices in terms of the steric
interactions that both isomers will experience in their respective chair conformations. (Klein Chapter 4)
8. (10 pts) Draw structures that match the following situations: (Klein Chapter 4)
a)
Newman projection of the least stable conformation of dodecane along the C-4 – C-5 bond axis.
b)
Newman projection of the most stable conformation of 2-methylheptane along C-3 – C-4.
5
9. (8 pts) In the following questions, one of the two species is less stable than the other. Indicate which is less
stable in each case and explain the reason for the decreased stability. (Klein Chapter 4)
10. (8 pts) Indicate which of the following molecules should be soluble in water and which will not be soluble.
Briefly explain your choices. (Klein Chapter 1)
6
Chemistry 3719
Practice Exam B1 Key
This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam and you may use molecular models as needed. Good Luck.
1. (8 pts) Fill in the ground state electron distribution for N (from the periodic table), then construct hybrid
orbital pictures for the highlighted N atoms that describe the orbitals used by N for bonding in each case.
(Klein Chapter 1)
1
2. (20 pts) For each of the following acid-base reactions, draw the conjugate acid and conjugate base that are
expected to be formed. Label the acids on each side of the equations with approximate pKa values, and
indicate in each case if you expect the reaction to favor the left-hand side, the right-hand side, or neither.
(Klein Chapter 3)
OH
a)
ONa
+
NaOH
R.H.S favored
pKa ~ 10
b)
+
CF3CH2OK
+
pKa ~ 16
L.H.S favored
H
N
+
C
C
pKa ~ 38
H
NH
pKa ~ 25
OLi
NH3
+
neither favored
pKa ~ 38
e)
CH3CH2OK
pKa < 16
KNH2
+
NLi
+
K
N
c)
d)
pKa ~ 16
CF3CH2OH
CH3CH2OH
H 2O
R.H.S favored
+
C
C
pKa ~ 38
OH
OH
OLi
+
+
O
O
pKa ~ 5
R.H.S favored
2
Li
pKa ~ 16
3. (15 pts) Provide acceptable names for the following molecules. Trivial or IUPAC names may be used as
appropriate. (Klein Chapter 4)
a)
CH3
H
CH2CH3
H3 C
2,3-dimethylpentane
H
CH3
b)
H
CH2CH(CH3)2
H
trans-1-isobutyl-3-isopropylcyclohexanol
c)
3,4,6-trimethylnonane
d)
Bicyclo[4.2.1]nonane
e)
1-(sec-butyl)-4-cyclobutyl-2-methylcyclopentane
3
4. (6 pts) Draw all of the isomeric alkanes that have the molecular formula C5H12 and give each of them a
suitable name. (Klein Chapter 4)
5. (6 pts) Provide any missing formal charges that are necessary in the following molecules. (Klein Chapter
1)
a.
b.
c.
N
O
6. (9 pts) Draw a second resonance structure for each of the following and indicate which structure you expect
to be more significant in each system. Be sure to put lone pairs in the correct places. (Klein Chapter 2)
4
7. (10 pts) For cis-1-t-butyl-2-methylcyclohexane and trans-1-t-butyl-2-methylcyclohexane, draw two ringflipped chair forms for each isomer, then indicate the preferred conformation for each of the two isomers,
and finally indicate which if the two isomers is more stable. Explain your choices in terms of the steric
interactions that both isomers will experience in their respective chair conformations. (Klein Chapter 4)
The trans isomer will be more stable since both of the large groups are able to be
equatorial thus avoiding any destabilizing 1,3-diaxial interactions. Both of the
conformations of the cis isomer will have a large group in an axial position.
8. (10 pts) Draw structures that match the following situations: (Klein Chapter 4)
a)
Newman projection of the least stable conformation of dodecane along the C-4 – C-5 bond axis.
b)
Newman projection of the most stable conformation of 2-methylheptane along C-3 – C-4.
5
9. (8 pts) In the following questions, one of the two species is less stable than the other. Indicate which is less
stable in each case and explain the reason for the decreased stability. (Klein Chapter 4)
10. (8 pts) Indicate which of the following molecules should be soluble in water and which will not be soluble.
Briefly explain your choices. (Klein Chapter 1)
Solubility is based on interactions between the solute and solvent and is generalized by
the term “like dissolve like” – here the OH groups are capable of hydrogen bonding with
water while the hydrophobic alkyl groups will repel. Large alkyl portions outweigh the
importance of the OH group and cause insolubility as listed; many OH groups (bottom
left) will enhance solubility.
6
Chemistry 3719
Practice Exam B2
This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam and you may use molecular models as needed. Good Luck.
1. (8 pts) Provide a detailed mechanism, using curved arrows to show the breaking and forming of bonds, that
accounts for the following conversion. (Klein Chapter 8)
1
2. (12 pts) Provide structures of the major and minor organic product(s) that are expected to be formed in each
of the following situations. (Klein Chapters 7-8)
a)
Br
NaOCH3
Br CH
3
b)
CH3OH
OTs
NaN3, DMF
c)
CH3
KO-tBu
d)
Cl
OH
e)
H3PO4, heat
Br
f)
NaCl
2
3. (9 pts) For each of the following pairs of molecules, identify any stereogenic centers, label them as having
the (R) or the (S) configuration, and then indicate the relationship between the two molecules; are they
enantiomers, diastereomers, or are they identical? (Klein Chapter 5)
a)
b)
c)
4. (8 pts) Give all of the expected organic products from the following reaction and label those products as
being major, minor, or very minor. Then give an explanation for your assignments. (Klein Chapter 8)
3
5. (12 pts) Give the major organic product formed under the following reaction conditions and then a detailed
mechanism, using curved arrows to show bonds being formed and broken, to describe the transformation.
(Klein Chapters 6-7)
Draw a reaction profile on the axes below for the formation of the organic product above that includes
structures of the reactant, any intermediate(s), and a transition state for the rate-determining step only.
Potential
energy
Reaction coordinate
4
6. (8 pts) Which isomer undergoes faster E2 reaction with base, cis-1-bromo-4-t-butyl cyclohexane or trans-1bromo-4-t-butylcyclohexane? Use diagrams to help with your explanation. (Klein Chapter 8)
7. (9 pts) Give each of the following molecules acceptable names; you may use trivial or IUPAC names for
substituents as needed. (Klein Chapters 7-8)
a)
H
Br
b)
I
Cl
c)
5
8. (8 pts) Give a complete mechanism that accounts for the following conversion. The optical rotation (i.e.
[α]D) of the starting material is +54°; what do you expect the rotation of the product to be, and why? (Klein
Chapters 5-7)
8. (8 pts) In the boxes provided, give a structure of a suitable organic starting material that would be needed to
produce the given product in each of the following cases. (Klein Chapters 7-8)
a)
KOt-Bu
CH2
H2SO4, heat
b)
c)
N3
NaN3 in DMF
H3 C
H2O
d)
6
OH
9. (18 pts) Answer each of the following questions by circling your choice and then giving a few words of
explanation for why you made that choice. (Klein Chapters 7-8)
a) Which of the following species is the better nucleophile? Why?
b) Which of the following compounds would react faster in a solvolysis reaction with CH3OH? Why?
c) Which of the following solvents would allow for faster SN2 reactions? Why?
d) Which of the following species is the better leaving group? Why?
e) Which of the following compounds would completely deprotonate ethanol? Why?
f) Which of the following compounds would react faster in SN2 reactions? Why?
7
Chemistry 3719
Practice Exam B2 Key
This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam and you may use molecular models as needed. Good Luck.
1. (8 pts) Provide a detailed mechanism, using curved arrows to show the breaking and forming of bonds, that
accounts for the following conversion. (Klein Chapter 8)
Alkyl migration to convert a secondary carbocation
Into a more stable tertiary carbocation
1
2. (12 pts) Provide structures of the major and minor organic product(s) that are expected to be formed in each
of the following situations. (Klein Chapters 7-8)
a)
Br
NaOCH3
+
major
Br CH
3
b)
(Zaitsev)
minor
H3C OCH
3
CH3OH
(racemic, via 3o carbocation)
N3
OTs
NaN3, DMF
(inversion through SN2)
c)
CH3
CH3
CH3
KO-tBu
d)
+
Cl
major
(Hoffman)
minor
OH
e)
H3PO4, heat
+
major
Br
f)
(Zaitsev)
minor
Cl
NaCl
(via 2o to 3o carbocation
rearrangment)
2
3. (9 pts) For each of the following pairs of molecules, identify any stereogenic centers, label them as having
the (R) or the (S) configuration, and then indicate the relationship between the two molecules; are they
enantiomers, diastereomers, or are they identical? (Klein Chapter 5)
a)
b)
c)
4. (8 pts) Give all of the expected organic products from the following reaction and label those products as
being major, minor, or very minor. Then give an explanation for your assignments. (Klein Chapter 8)
3
5. (12 pts) Give the major organic product formed under the following reaction conditions and then a detailed
mechanism, using curved arrows to show bonds being formed and broken, to describe the transformation.
(Klein Chapters 6-7)
Draw a reaction profile on the axes below for the formation of the organic product above that includes
structures of the reactant, any intermediate(s), and a transition state for the rate-determining step only.
+
OH2
potential
energy
+
R.D.S.
OH
OH2
Reaction coordinate
4
6. (8 pts) Which isomer undergoes faster E2 reaction with base, cis-1-bromo-4-t-butyl cyclohexane or trans-1bromo-4-t-butylcyclohexane? Use diagrams to help with your explanation. (Klein Chapter 8)
7. (9 pts) Give each of the following molecules acceptable names; you may use trivial or IUPAC names for
substituents as needed. (Klein Chapters 7-8)
a)
H
(E)-3-bromo-5-methylhept-2-ene
Br
(S)-5-iodo-3,3-dimethylcyclopent-1-ene
b)
I
Cl
c)
1-chloro-2-propylcyclohex-1-ene
5
8. (8 pts) Give a complete mechanism that accounts for the following conversion. The optical rotation (i.e.
[α]D) of the starting material is +54°; what do you expect the rotation of the product to be, and why? (Klein
Chapters 5-7)
Br
OH
H2O
CH3
CH3
OH2
OH2
H
O H
H
O H
H
CH3
OH2
CH3
CH3
=
CH3
The chiral starting bromide converts to an achiral product so [α]D should be 0°.
8. (8 pts) In the boxes provided, give a structure of a suitable organic starting material that would be needed to
produce the given product in each of the following cases. (Klein Chapters 7-8)
KOt-Bu
a)
I
CH2
E2
OH
H2SO4, heat
b)
E1
Br
c)
N3
NaN3 in DMF
S N2
H3C
d)
H3 C
Br
H2O
SN1
6
OH
9. (18 pts) Answer each of the following questions by circling your choice and then giving a few words of
explanation for why you made that choice. (Klein Chapters 7-8)
a) Which of the following species is the better nucleophile? Why?
b) Which of the following compounds would react faster in a solvolysis reaction with CH3OH? Why?
c) Which of the following solvents would allow for faster SN2 reactions? Why?
d) Which of the following species is the better leaving group? Why?
e) Which of the following compounds would completely deprotonate ethanol? Why?
f) Which of the following compounds would react faster in SN2 reactions? Why?
7
Chemistry 3719
Practice Exam B3
This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam and you may use molecular models as needed. Good Luck.
1. (7 pts) Give a detailed mechanism that shows the main steps that lead to the two products in the following
reaction. Include structures of any intermediates that are formed. (Klein Chapter 11)
1
2. (7 pts) Give the expected major product and then provide a detailed mechanism, using curved arrows to
show the breaking and forming of bonds, for the following reaction. (Klein Chapter 10)
3. (7 pts) Give the expected major and minor products formed under the following conditions. Then give a
mechanism for the formation of both the major and minor products. (Klein Chapter 11)
2
4. (18 pts) Provide structures of the major and minor organic product(s) that are expected to be formed in each
of the following situations. When more than one reaction is involved, a product from each is required.
(Klein Chapters 9-11)
Br2, heat
a)
CH3
dilute H2SO4
b)
H2, Pt
c)
CH3
1. O3
d)
2. Zn, H2O
HBr
e)
Br
f)
NaOCH3
CH3OH
3
5. (8 pts) In the boxes provided, give a structure of the organic starting material that would be needed to
provide the given product in each of the following cases. (Klein Chapters 10-11)
Br
a)
Br2, heat
excess HBr
b)
Br Br
Br
c)
d)
CH3CO3H
O
6. (9 pts) Give the major product formed from free radical bromination of the following molecules and then
give a name for each of those products. (Klein Chapter 11)
a) Methylcyclopentane
b) 2,3-Dimethylbutane
c) 2,2,4,4-Tetramethylpentane
4
7. (9 pts) Give each of the following compounds acceptable names. You may use either the IUPAC system or
the common names for substituents. Watch out for any stereochemical issues (i.e cis/trans or R/S). (Klein
Chapter 10)
a.
b.
c.
8. (6 pts) In each of the series of molecules below, circle the most stabilized species, and then give a few
words of explanation for your choice. (Klein Chapters 3-11)
a)
b)
c)
5
9. (7 pts) Give all of the possible monobrominated products formed under the following conditions. Then
provide a detailed mechanism, pushing curved arrows to describe all important bond-forming and bondbreaking events, that accounts for the formation of the major product in the following reaction. (Klein
Chapter 11)
10. (7 pts) Provide a detailed mechanism for the following reaction that explains the bond-forming and bondbreaking steps on the way to the product. (Klein Chapter 9)
6
11. (7 pts) Provide a detailed mechanism, pushing curved arrows to describe bonds forming and breaking, that
accounts for the formation of both products in the following reaction. (Klein Chapter 9)
12. (8 pts) Give the major and minor final products formed in each of the following situations, and then give an
explanation for the different outcomes. (Klein Chapter 9)
a)
b)
7
Chemistry 3719
Practice Exam B3 Key
This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam and you may use molecular models as needed. Good Luck.
1. (7 pts) Give a detailed mechanism that shows the main steps that lead to the two products in the following
reaction. Include structures of any intermediates that are formed. (Klein Chapter 11)
1
2. (7 pts) Give the expected major product and then provide a detailed mechanism, using curved arrows to
show the breaking and forming of bonds, for the following reaction. (Klein Chapter 10)
3. (7 pts) Give the expected major and minor products formed under the following conditions. Then give a
mechanism for the formation of both the major and minor products. (Klein Chapter 11)
2
4. (18 pts) Provide structures of the major and minor organic product(s) that are expected to be formed in each
of the following situations. When more than one reaction is involved, a product from each is required.
(Klein Chapters 9-11)
a)
Br
Br2, heat
(via 3o radical)
H3C OH
CH3
dilute H2SO4
b)
(via 3o carbocation)
H
H2, Pt
(via syn addition)
c)
H
CH3
CH3
1. O3
d)
CH3
O
1.
2. Zn, H2O
O
O
2.
O
O
H
Br
HBr
e)
(via 3o carbocation)
Br
f)
NaOCH3
(more highly substituted
alkene formed - Zaitsev)
CH3OH
3
5. (8 pts) In the boxes provided, give a structure of the organic starting material that would be needed to
provide the given product in each of the following cases. (Klein Chapters 10-11)
H
a)
Br
Br2, heat
excess HBr
b)
Br Br
c)
Br
Na
d)
CH3CO3H
O
6. (9 pts) Give the major product formed from free radical bromination of the following molecules and then
give a name for each of those products. (Klein Chapter 11)
a) Methylcyclopentane
b) 2,3-Dimethylbutane
c) 2,2,4,4-Tetramethylpentane
4
7. (9 pts) Give each of the following compounds acceptable names. You may use either the IUPAC system or
the common names for substituents. Watch out for any stereochemical issues (i.e cis/trans or R/S). (Klein
Chapter 10)
OH
a.
(R,Z)-hept-4-en-1-yn-3-ol
b.
Br
(R)-3-bromo-3-ethynylcyclopent-1-ene
c.
(R)-4-chlorohex-1-yne
Cl
8. (6 pts) In each of the series of molecules below, circle the most stabilized species, and then give a few
words of explanation for your choice. (Klein Chapters 3-11)
a)
b)
c)
5
9. (7 pts) Give all of the possible monobrominated products formed under the following conditions. Then
provide a detailed mechanism, pushing curved arrows to describe all important bond-forming and bondbreaking events, that accounts for the formation of the major product in the following reaction. (Klein
Chapter 11)
10. (7 pts) Provide a detailed mechanism for the following reaction that explains the bond-forming and bondbreaking steps on the way to the product. (Klein Chapter 9)
6
11. (7 pts) Provide a detailed mechanism, pushing curved arrows to describe bonds forming and breaking, that
accounts for the formation of both products in the following reaction. (Klein Chapter 9)
12. (8 pts) Give the major and minor final products formed in each of the following situations, and then give an
explanation for the different outcomes. (Klein Chapter 9)
a)
The outcome here is governed mainly by the relative steric interactions in the transition states of
the hydroboration step. The large –BR2 group will avoid the more crowded end of the alkene; the
oxidation step retains the regiochemistry and stereochemistry (syn addition) from the first step.
b)
In the acid-catalyzed addition of H2O to this unsymmetrical alkene the product distribution
depends upon the type of carbocation that could be formed; the major product will be formed via
the tertiary carbocation, which is more stabilized by hyperconjugation than the secondary (the
Markovnikoff rule).
7
Chemistry 3719
Practice Exam C1
This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam and you may use molecular models as needed. Good Luck.
1. (6 pts) Label all of the sp2 hybridized atoms within the following molecules. (Klein Chapter 1)
a)
O
H
NCH3
b)
O
c)
O
1
2. (15 pts) Draw the required structures in each of the following situations. (Klein Chapter 4)
a) The highest energy chair conformation of trans-1,2-dibromocyclohexane
b) A Newman projection of a gauche conformation of n-octane along the C-2 – C-3 bond axis.
c) The less stable isomer of 1,2-diisopropylcyclopropane.
d) A Newman projection of the most stable conformation of n-hexane along the C-3 – C-4 bond axis
e) A boat conformation of cyclohexane.
2
3. (15 pts) Give acceptable names for the following molecules. Trivial or IUPAC names may be used for
substituents. (Klein Chapter 4)
a)
b)
c)
CH(CH3)2
d)
C(CH3)3
e)
3
4. (15 pts) Give the products from each of the following acid-base reactions. Then give the acids on each side
of the equations approximate pKa values and indicate in each case if you expect the reaction to be
exothermic, endothermic, or approximately thermoneutral in each case. (Klein Chapter 3)
a)
+
Li
H2 O
OLi
b)
OH
+
c)
CH3 C C H
+
CH3CH2NHLi
+
LiN(CH3)2
d)
N
H
OH
e)
+
CH3CH2CH2OK
4
5. (9 pts) Draw acceptable structures for each of the following molecules. (Klein Chapter 4)
a) trans-1-Ethyl-3-isopropylcyclopentane
b) Cyclopentylcyclohexane
c) 2,4,4-Trimethyl-3-octanol
6. (10 pts) Draw all of the isomers possible for C6H14 and then give each structure an acceptable name. (Klein
Chapter 4)
5
7. (8 pts) For the highlighted atom in the following molecules, fill in the ground state electronic configuration
on the left, and then draw a picture on the right of the hybridization model that best explains the bonding of
the highlighted atoms. (Klein Chapter 1)
8. (6 pts) Which of the two molecules below is the stronger acid? Give their approximate pKa values and
explain your choice in terms of the structures and relative stabilities of the respective conjugate bases.
(Klein Chapter 3)
O
OH
OH
6
9. (6 pts) Draw a second resonance structure for the following anions and then an overall resonance hybrid for
each. (Klein Chapter 2)
10. (10 pts) Consider the cis- and trans- isomers 1-t-butyl-3-ethylcyclohexane. (Klein Chapter 4)
a. Draw the lowest energy ring conformation for both isomers and explain your choices.
b. Indicate which isomer is less stable and explain your reasoning using a diagram to highlight any
destabilizing interactions.
7
Chemistry 3719
Practice Exam C1 Key
This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam and you may use molecular models as needed. Good Luck.
1. (6 pts) Label all of the sp2 hybridized atoms within the following molecules. (Klein Chapter 1)
a)
O
H
NCH3
b)
O
c)
O
1
2. (15 pts) Draw the required structures in each of the following situations. (Klein Chapter 4)
a) The highest energy chair conformation of trans-1,2-dibromocyclohexane
Br
H
H
Br
b) A Newman projection of a gauche conformation of n-octane along the C-2 – C-3 bond axis.
c) The less stable isomer of 1,2-diisopropylcyclopropane.
d) A Newman projection of the most stable conformation of n-hexane along the C-3 – C-4 bond axis
H
H
CH2CH3
H
H
CH2CH3
e) A boat conformation of cyclohexane.
2
3. (15 pts) Give acceptable names for the following molecules. Trivial or IUPAC names may be used for
substituents. (Klein Chapter 4)
a)
6-ethyl-3,5,5-trimethylnonane
b)
bicyclo[5.3.0]decane
c)
6-isopropyl-2,5-dimethylundecane
CH(CH3)2
d)
trans-1-(tert-butyl)-3-isopropylcyclohexane
C(CH3)3
e)
6-cyclopropyl-2,3-dimethylheptane
3
4. (15 pts) Give the products from each of the following acid-base reactions. Then give the acids on each side
of the equations approximate pKa values and indicate in each case if you expect the reaction to be
exothermic, endothermic, or approximately thermoneutral in each case. (Klein Chapter 3)
exothermic
a)
+
Li
base
H2 O
OH
thermoneutral
OH
+
b)
LiOH
pKa ~ 50
acid: pKa ~ 16
OLi
+
H
OLi
+
base
pKa ~ 16
acid: pKa ~ 16
exothermic
c)
CH3 C C H
+
acid: pKa ~ 25
CH3 C CLi
LiN(CH3)2
+
base
HN(CH3)2
pKa ~ 38
thermoneutral
d)
CH3CH2NHLi
base
+
N
H
CH3CH2NH2
acid: pKa ~ 38
pKa ~ 38
OH
+
N
Li
OK
exothermic
e)
+
acid: pKa ~ 10
CH3CH2CH2OK
+
CH3CH2CH2OH
acid: pKa ~ 16
base
4
5. (9 pts) Draw acceptable structures for each of the following molecules. (Klein Chapter 4)
a) trans-1-Ethyl-3-isopropylcyclopentane
b) Cyclopentylcyclohexane
c) 2,4,4-Trimethyl-3-octanol
6. (10 pts) Draw all of the isomers possible for C6H14 and then give each structure an acceptable name. (Klein
Chapter 4)
5
7. (8 pts) For the highlighted atom in the following molecules, fill in the ground state electronic configuration
on the left, and then draw a picture on the right of the hybridization model that best explains the bonding of
the highlighted atoms. (Klein Chapter 1)
8. (6 pts) Which of the two molecules below is the stronger acid? Give their approximate pKa values and
explain your choice in terms of the structures and relative stabilities of the respective conjugate bases.
(Klein Chapter 3)
The electron-withdrawing C=O in the carboxylic acid makes the OH proton
more positive than in the alcohol, and the C=O also allows the charge in the
anion to delocalize thus making the conjugate base more stable.
6
9. (6 pts) Draw a second resonance structure for the following anions and then an overall resonance hybrid for
each. (Klein Chapter 2)
10. (10 pts) Consider the cis- and trans- isomers 1-t-butyl-3-ethylcyclohexane. (Klein Chapter 4)
a. Draw the lowest energy ring conformation for both isomers and explain your choices.
This conformation of the cis isomer can have both substituents equatorial thus avoiding
any destabilizing 1,3-diaxial interactions that would occur in the “ring-flipped”
conformation. The trans isomer has to have one substituent axial and will prefer the
conformation in which the smaller ethyl group is axial and not the larger t-butyl group,
which would inevitably have significantly more destabilizing 1,3-interactions.
b. Indicate which isomer is less stable and explain your reasoning using a diagram to highlight any
destabilizing interactions.
The trans isomer is less stable here since in either ring conformation one of the bulky
groups will have to be in an axial position thus destabilizing the system due to 1,3-diaxial
interactions (below).
7
Chemistry 3719
Practice Exam C2
This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam and you may use molecular models as needed. Good Luck.
1) (10 pts) Give a complete mechanism for how both products are formed in the following reaction. Which
product do you expect to be major and which minor? Briefly explain your answer. (Klein Chapter 8)
1
2) (18 pts) Give organic product(s), labeling major and minor where applicable, for the following reactions.
(Klein Chapters 7-8)
OH
a)
H2SO4,
H3 C
Br
b)
KCN, DMF
c)
OH
O
HCl
CH3
Cl
NaOCH3
d)
CH3OH,
e)
OH
HBr
OSO2CF3
f)
H3 C
KOt-Bu
2
3) (10 pts) Give the major organic product expected below, then a draw the reaction profile (potential energy
vs. reaction coordinate) for the conversion that includes pictures of the transition state(s) involved. (Klein
Chapters 6-7)
Potential
energy
Reaction coordinate
4) (9 pts) Give acceptable names for each of the following molecules. (Klein Chapters 5-8)
a)
Br
OH
b)
OH
Cl
c)
OH
3
5) (8 pts) Give the major organic products formed under the following conditions and a detailed mechanism
that explains their formation. Will the product mixture have an optical rotation or will [α]D = 0? (Klein
Chapter 7)
6) (9 pts) Give structures for each of the following molecules. (Klein Chapters 7-8)
a) (E)-4-Methyl-3-hexen-2-ol
b) 1-Bromo-5-tert-butylcyclohex-1-ene
c) trans-2-Isopropenylcyclopentanol
4
7) (12 pts) Tamiflu® has been developed by Roche Pharmaceuticals to alleviate the symptoms caused by the
influenza virus. The 14-step synthesis of Tamiflu® begins with the chiral natural product shikimic acid
(below). Identify all of the stereocenters in both shikimic acid and Tamiflu® and label them as having the
(R) or (S) configuration. (Klein Chapter 5)
HO
OH
HO
O
HO
shikimic acid
Roche
Pharmaceuticals
14 steps
H2 N
O
H
N
O
O
O
Tamiflu
8) (8 pts) Working out the configurations of the chiral centers (i.e. R or S) will help in the following questions.
(Klein Chapter 5)
a. Convert the following “wedge-dash” depiction into a Fischer projection.
b. What is the relationship between the following molecules (same, enantiomers, diastereomers)?
5
9) (10 pts) Provide explanations, using Newman projections, to explain the following product outcomes. (Klein
Chapter 8)
a)
b)
10) (6 pts) In each of the following cases, circle your choice and then give a few words of explanation for why
you made that choice. (Klein Chapter 7)
a. Reacts faster in SN2 reactions with NaN3 as the nucleophile?
b. Better solvent in SN1 reactions?
c. Better nucleophile in SN2 reactions?
6
Chemistry 3719
Practice Exam C2 Key
This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam and you may use molecular models as needed. Good Luck.
1) (10 pts) Give a complete mechanism for how both products are formed in the following reaction. Which
product do you expect to be major and which minor? Briefly explain your answer. (Klein Chapter 8)
OH
H2SO4
+
heat
H OH2
-H3O
-H3O
H2O
OH2
H
-H2O
H
H2O
Rearrangement occurs where the more stable tetrasubstituted alkene is preferred over
2
trisubstituted alternative; sp hybrid C in alkenes is stabilized by alkyl groups through
induction, thus the more alkyl groups the better the alkene.
1
2) (18 pts) Give organic product(s), labeling major and minor where applicable, for the following reactions.
(Klein Chapters 7-8)
OH
a)
H
H2SO4,
H3C
H
+
H3C
H 3C
E1 - Zaitsev
major
Br
CN
b)
c)
minor
KCN, DMF
OH
O
HCl
CH3
only inverted
product via SN2
Cl
O
CH3
CH3
O
+
Cl
racemic mixture via SN1
Cl
NaOCH 3
d)
+
CH3OH,
major
E2 - Zaitsev
OH
HBr
minor
Br
only product
via SN2
e)
OSO2CF3
f)
H3C
KOt-Bu
H 3C
H3C
+
E2 - Hofmann
major
2
minor
3) (10 pts) Give the major organic product expected below, then a draw the reaction profile (potential energy
vs. reaction coordinate) for the conversion that includes pictures of the transition state(s) involved. (Klein
Chapters 6-7)
HCl
HO
Cl
SN2
H
Potential
energy
(+ H2O)
+ H
O
H
H
Cl
Cl
-
-
H
H
O
+
HO
+ HCl
H2O
Cl
Reaction coordinate
4) (9 pts) Give acceptable names for each of the following molecules. (Klein Chapters 5-8)
a)
b)
c)
3
5) (8 pts) Give the major organic products formed under the following conditions and a detailed mechanism
that explains their formation. Will the product mixture have an optical rotation or will [α]D = 0? (Klein
Chapter 7)
In this SN1 reaction the leaving group breaks away to leave a flat carbocation that has three
different alkyl groups attached. When the bromide nucleophile attacks it may do so from
either face of the cation to produce enantiomeric products in approximately equal amounts.
The optical rotation of this racemic mixture will therefore be zero as the rotations of the
enantiomers will cancel.
6) (9 pts) Give structures for each of the following molecules. (Klein Chapters 7-8)
a) (E)-4-Methyl-3-hexen-2-ol
b) 1-Bromo-5-tert-butylcyclohex-1-ene
c) trans-2-Isopropenylcyclopentanol
4
7) (12 pts) Tamiflu® has been developed by Roche Pharmaceuticals to alleviate the symptoms caused by the
influenza virus. The 14-step synthesis of Tamiflu® begins with the chiral natural product shikimic acid
(below). Identify all of the stereocenters in both shikimic acid and Tamiflu® and label them as having the
(R) or (S) configuration. (Klein Chapter 5)
(R)
HO
OH
HO
O
(S)
HO
(R)
shikimic acid
Roche
Pharmaceuticals
14 steps
(S)
H2 N
O
H
N
O
O
(R)
O
(R)
Tamiflu
8) (8 pts) Working out the configurations of the chiral centers (i.e. R or S) will help in the following questions.
(Klein Chapter 5)
a. Convert the following “wedge-dash” depiction into a Fischer projection.
b. What is the relationship between the following molecules (same, enantiomers, diastereomers)?
5
9) (10 pts) Provide explanations, using Newman projections, to explain the following product outcomes. (Klein
Chapter 8)
a)
b)
10) (6 pts) In each of the following cases, circle your choice and then give a few words of explanation for why
you made that choice. (Klein Chapter 7) F07 Exam 3
a. Reacts faster in SN2 reactions with NaN3 as the nucleophile?
b. Better solvent in SN1 reactions?
c. Better nucleophile in SN2 reactions?
6
Chemistry 3719
Practice Exam C3
This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam and you may use molecular models as needed. Good Luck.
1. (9 pts) Give the major and minor alkyl halide products expected from the following reaction and then show
a mechanism (using curved arrows) that describes how the major product is formed during the reaction.
(Klein Chapter 11)
1
2. (18 pts) Give the expected major products from each of the following reactions. When more than one set of
reagents are given the major product from each step is required. Where stereochemistry is an issue, label the
products as being either single stereoisomers, enantiomers, or diastereomers. (Klein Chapters 7-10)
a.
1. O3
2. Zn, H2O
Cl
b.
NaCN
DMSO, 50 oC
1. H-B(C6H11)2
c.
2. NaOH, H2O2
Br2
d.
e.
f.
CH3CO3H
H
C
C
H
1. NaNH2
2. CH3CH2I
2
3. (8 pts) Give the major and minor product(s) from the following reaction and then a complete mechanism
(using curved arrows) for the formation of the major product. Explain briefly why this product is major.
(Klein Chapter 9)
4. (12 pts) Draw acceptable structures for each of the following molecules. (Klein Chapters 7-10)
a. (4S,5S)-5,7-dimethyl-1-octyn-4-ol
b. (2R,3S,Z)-2-bromo-5-fluoro-3-methyl-4-heptene
c. (1R,2S)-1-bromo-2-isopropylcyclohexane
3
5. (12 pts) Provide the major product from each step of the following reaction sequence: (Klein Chapter 10)
6. (8 pts) Give an explanation for the different product outcomes in the following reactions. (Klein Chapter
11)
4
7. (8 pts) Draw the organic product produced under the following ozonolysis conditions; then draw a detailed
mechanism for its formation. (Klein Chapter 9)
8. (8 pts) In each of the following reactions give a mechanistic explanation that accounts for the observed
regiochemistry and/or stereochemistry in each product. (Klein Chapter 9)
a. Explain the observed stereochemistry and regiochemistry in the following hydroboration:
b. Explain the observed stereochemistry in the following addition of Br2:
5
9. (9 pts) Provide a complete mechanism for the following conversion. (Klein Chapter 9)
10. (8 pts) Give the expected product from the following portion of the hydroboration-oxidation sequence and a
mechanism for its formation. Be careful to account for any important stereochemical issues. (Klein Chapter
9)
6
Chemistry 3719
Practice Exam C3 Key
This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam and you may use molecular models as needed. Good Luck.
1. (9 pts) Give the major and minor alkyl halide products expected from the following reaction and then show
a mechanism (using curved arrows) that describes how the major product is formed during the reaction.
(Klein Chapter 11)
1
2. (18 pts) Give the expected major products from each of the following reactions. When more than one set of
reagents are given the major product from each step is required. Where stereochemistry is an issue, label the
products as being either single stereoisomers, enantiomers, or diastereomers. (Klein Chapters 7-10)
a.
1. O3
O O
1.
Cl
+
CN
NaCN
SN2 reaction only gives the one
(inverted) product
o
DMSO, 50 C
1. H-B(C6H11)2
c.
O
O
2. Zn, H2O
b.
O
2.
1.
H
B(C6H11)2
2.
H
OH
2. NaOH, H2O2
Br
Br
Br2
d.
+
Br
Br
(R,R)
(S,S)
Enantiomers formed (50/50)
e.
CH3CO3H
+
O
O
Diastereomers formed (~50/50)
f.
H
C
C
H
1. NaNH2
H
1.
2. CH3CH2I
2
C
H
C
2.
C
CCH2CH3
3. (8 pts) Give the major and minor product(s) from the following reaction and then a complete mechanism
(using curved arrows) for the formation of both products. Explain briefly why one product is major. (Klein
Chapter 9)
The major product in this electrophilic addition reaction is produced via
the more stabilized tertiary carbocation, which is preferred over the
alternative secondary carbocation, due to increased hyperconjugation;
the tertiary carbocation has more adjacent (beta) σ bonds, which are
able to share electron density with the electron-poor positive carbon.
4. (12 pts) Draw acceptable structures for each of the following molecules. (Klein Chapters 7-10)
a. (4S,5S)-5,7-dimethyl-1-octyn-4-ol
b. (2R,3S,Z)-2-bromo-5-fluoro-3-methyl-4-heptene
c. (1R,2S)-1-bromo-2-isopropylcyclohexane
Br
3
5. (12 pts) Provide the major product from each step of the following reaction sequence: (Klein Chapter 10)
1. Br2 in CCl4
2. excess NaNH2
then H+ quench
3. CH3CH2CH2CH2Li
4. CH3CH2CH2Br
5. Na, liq. NH3
6. CH3CO3H
1.
4.
Br
Br
2.
3.
5.
6.
Na
O
6. (8 pts) Give an explanation for the different product outcomes in the following reactions. (Klein Chapter
11)
The difference in the product distributions is due to the difference in the stability of
the Br and the Cl radicals. The Br radical is more stable and is therefore able to be
more selective when it comes to abstracting a hydrogen atom to produce a carbon
o
radical. In this case the more stabilized 2 radical is formed preferably leading to
o
the 2 alkyl halide being the vast majority of the product. The Cl radical is much
o
more reactive, and therefore less selective, resulting in significantly more of the 1
alkyl halide product being formed with Cl2 as the halogen radical source.
4
7. (8 pts) Draw the organic product produced under the following ozonolysis conditions; then draw a detailed
mechanism for its formation. (Klein Chapter 9)
8. (8 pts) In each of the following reactions give a mechanistic explanation that accounts for the observed
regiochemistry and/or stereochemistry in each product. (Klein Chapter 9)
a. Explain the observed stereochemistry and regiochemistry in the following hydroboration:
This reaction involves a syn addition of the BH3 molecule hence the shown cis
stereochemical outcome. The regiochemical preference is explained by the smaller H
bonding to the less accessible carbon of the alkene and the larger BH2 group adding to
the less hindered carbon.
b. Explain the observed stereochemistry in the following addition of Br2:
This addition reaction involves the formation of a carbocation that is stabilized by
donation of electron density from the first Br that has added (bromonium ion). The large
Br then blocks one face of the molecule such that the bromide ion may only attack from
the opposite face, hence the trans stereochemistry.
5
9. (9 pts) Provide a complete mechanism for the following conversion.
10. (8 pts) Give the expected product from the following portion of the hydroboration-oxidation sequence and a
mechanism for its formation. Be careful to account for any important stereochemical issues. (Klein Chapter
9)
The migration step is concerted and the initial stereochemistry of the addition (syn) is
retained to give the product shown.
6
Chemistry 3719, Fall 2013
Exam 1
Student Name:
“Y” Number:
This exam is worth 100 points out of a total of 700 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam. Good Luck!
1. (8 pts) For the highlighted atom in the following molecules, fill in the ground state electronic configuration
from the periodic table on the left, and then draw a picture on the right of the hybridization model that best
explains the atomic orbitals used in bonding by the highlighted atoms.
O
H
Energy
hybridize
Energy
hybridize
H C N
1
2. (10 pts) Provide the required values for each of the following species as indicated.
a.
Give each of the following atoms an approximate electronegativity value:
b. Give each of the following acids an approximate pKa value:
3. (9 pts) In each of the following pairs of molecules one of the two is more stable than the other. Circle the
more stable molecule and then briefly explain your choices in the space on the right.
Li
OLi
a.
vs.
CH2
b.
O
vs.
O
c.
O
F
F
OLi
F
vs.
H
H
OLi
H
2
4. (9 pts) Provide each of the following alkane derivatives with an acceptable name. You may use either the
common or IUPAC names for substituents.
a.
b.
c.
5. (9 pts) For the following systems, draw all of the other important resonance structures, including any lone
pairs, and then a resonance hybrid for each molecule.
a.
O
b.
O
H
c.
3
6. (12 pts) Give the products expected from each of the following acid-base reactions. Then label each acid
with an approximate pKa and indicate whether deprotonation will be complete or incomplete in each case.
OH
a.
+ KOCH2CH3
OH
b.
c.
+
NLi
NaO
+
7. (8 pts) The following molecule has been designed as a synthetic intermediate in the formation of glutathione
drug analogs. Identify each of the eight (8) functional groups contained within the molecule.
4
8. (9 pts) In each of the pairs of compounds below, indicate whether the structures are related as stereoisomers,
constitutional isomers, or are the same compound. Then circle the more stable of the two structures and give
a few words of explanation for your choices.
CH3
a.
and
H3C
CH3
CH3
b.
H
H
CH3
H3C
H
CH3
and
H3C
H
c.
H
H
H
H
and
9. (8 pts) For each of the following structures, add any missing lone pairs that are needed and label any formal
charges that are necessary.
a.
O
b.
O
H
O
N
O
c.
d.
O
O
O
5
O
10. (9 pts) Draw Newman depictions that correspond to the following conformations.
a. The most stable conformation of 2-methyloctane along the C-4–C-5 bond.
b. The least stable conformation of 2,2-dimethylhexane along the C-3–C-4 bond.
c. A gauche conformation for hexylcyclopropane along the C-3–C-4 bond of the hexyl chain.
11. (9 pts) For each of the three molecules below, indicate whether you expect them to be a solid, liquid, or gas
at room temperature and whether you expect them to dissolve in water or not. Explain your choices briefly.
HO
O
HO
HO
O
HO
O
OH
OH
OH
OH
OH
anthracene
sucrose
6
1-octanol
Chemistry 3719, Fall 2013
Exam 1 – Key
Student Name:
“Y” Number:
This exam is worth 100 points out of a total of 700 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam. Good Luck!
1. (8 pts) For the highlighted atom in the following molecules, fill in the ground state electronic configuration
from the periodic table on the left, and then draw a picture on the right of the hybridization model that best
explains the atomic orbitals used in bonding by the highlighted atoms.
lone pairs
O
H
hybridize
Energy
to
bonds
sp3
to
lone pair to
H C N
hybridize
Energy
1
bonds
bond
p
sp
2. (10 pts) Provide the required values for each of the following species as indicated.
a.
Give each of the following atoms an approximate electronegativity value:
b. Give each of the following acids an approximate pKa value:
3. (9 pts) In each of the following pairs of molecules one of the two is more stable than the other. Circle the
more stable molecule and then briefly explain your choices in the space on the right.
Li
OLi
a.
A negative charge on a highly electronegative
atom such as O is more stable than on C
vs.
CH2
b.
O
The lone pair on the right will delocalize such
that some of the charge will be on O and not C
vs.
O
c.
O
F
F
OLi
F
vs.
H
H
The highly electronegative F atoms will help
to spread negative charge through induction
OLi
H
2
4. (9 pts) Provide each of the following alkane derivatives with an acceptable name. You may use either the
common or IUPAC names for substituents.
a.
bicyclo[3.3.3]undecane
b.
2-isobutyl-5-isopropyl-1,1-dimethylcycloheptane
c.
3,5-diethyl-6,7,7-trimethyldecane
5. (9 pts) For the following systems, draw all of the other important resonance structures, including any lone
pairs, and then a resonance hybrid for each molecule.
a.
O
O
O
O
-
b.
O
H
O
H
O
+H
O
+
H
+
c.
+
+
+
3
6. (12 pts) Give the products expected from each of the following acid-base reactions. Then label each acid
with an approximate pKa and indicate whether deprotonation will be complete or incomplete in each case.
OH
OK
a.
+ KOCH2CH3
pKa = 10
OH
b.
+ HOCH2CH3
K ~ 106
complete
deprotonation
pKa = 16
ONa
+
+
NaO
K~1
incomplete
deprotonation
pKa = 16
HO
pKa = 16
Li
c.
NLi
+
NH
pKa = 25
K ~ 1013
complete
deprotonation
+
pKa = 38
7. (8 pts) The following molecule has been designed as a synthetic intermediate in the formation of glutathione
drug analogs. Identify each of the eight (8) functional groups contained within the molecule.
4
8. (9 pts) In each of the pairs of compounds below, indicate whether the structures are related as stereoisomers,
constitutional isomers, or are the same compound. Then circle the more stable of the two structures and give
a few words of explanation for your choices.
CH3
a.
and
H3C
CH3
CH3
b.
H
H
CH3
H3C
H
CH3
Stereoisomers; having both CH3
groups on opposite sides of the
molecule reduces steric strain
and
H3C
H
c.
H
H
H
Same compound; right-hand is
more stable since both groups
are equatorial thus avoiding 1,3diaxial interactions
H
Constitutional isomers; right-hand
is more stable since it will have
less ring strain (no cyclopropane)
and
9. (8 pts) For each of the following structures, add any missing lone pairs that are needed and label any formal
charges that are necessary.
a.
O
b.
O
H
O
N
O
c.
d.
O
O
O
5
O
10. (9 pts) Draw Newman depictions that correspond to the following conformations.
a. The most stable conformation of 2-methyloctane along the C-4–C-5 bond.
b. The least stable conformation of 2,2-dimethylhexane along the C-3–C-4 bond.
c. A gauche conformation for hexylcyclopropane along the C-3–C-4 bond of the hexyl chain.
11. (9 pts) For each of the three molecules below, indicate whether you expect them to be a solid, liquid, or gas
at room temperature and whether you expect them to dissolve in water or not. Explain your choices briefly.
HO
O
HO
HO
O
HO
O
OH
OH
OH
OH
OH
anthracene
sucrose
1-octanol
Anthracene is a solid since it has the formula C14H10 and there will be significant intermolecular
dispersion forces holding molecules to each other. This compound is very non-polar so it would
not be expected to be soluble in water.
Sucrose has many OH groups which will allow H-bonding between molecules and cause this to be
a solid. The OH groups also make the compound polar and, combined with the H-bonding, will
make this material very soluble in water.
1-Octanol is a liquid since the greasy chain will only allow for weak intermolecular forces but the
OH group will give some H-bonding. The non-polar alkyl chain will outweigh the OH group so
this alcohol would not be expected to be soluble in water.
6
Chemistry 3719, Fall 2013
Exam 2
Student Name:
“Y” Number:
This exam is worth 100 points out of a total of 700 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam. Good Luck!
1. (10 pts) Draw two chair conformations for cis-1-t-butyl-4-ethylcyclohexane that are related through a ringflip. Then circle which conformation you expect to be more stable and explain why. Then do the same for
the trans isomer and, finally, indicate whether the cis or trans isomer should be more stable overall and
explain your choice.
1
2. (15 pts) Give the expected products, major and minor where applicable, in each of the following situations.
Be sure to take into account any changes in stereochemistry that may occur. If more than one set of reagents
is employed, product(s) from each step is/are required.
CH3
Br
NaCN, DMSO
a.
Br
KOC(CH3)3
b.
H
H3C
OH
c.
SO2Cl
pyridine
2. NaSH, DMSO
O
O
1.
CH3
I
d.
OH
e.
CH3OH
NaNH2, DMSO
Br
2
3. (9 pts) Provide each of the following molecules with an acceptable name. You may use either the common
or IUPAC names for substituents and be careful to include any stereochemical descriptors where needed.
Cl
a.
CH3
b.
H
Br
F
H
CH2CH3
c.
F
4. (10 pts) On the axes given below, draw a complete reaction profile for the following reaction that includes
diagrams of all intermediates and transition states involved.
3
5. (9 pts) In the boxes provided, identify the type of arrow-pushing process in each step within the following
reaction mechanisms (i.e. nucleophilic attack, leaving group leaving, proton transfer, or rearrangement).
a.
Br
H Br
H
b.
H
OH
OH2
H OH2
c.
Br
H
- H2O
H
H
Br
H2O
- Br
O
H
H2O
H
OH
H2O
6. (9 pts) The following solvolysis conditions give two major products in equal amounts and, when measured
for the mixture, []D = 0. Provide the products and a mechanism for this process, as well as an explanation
for the optical rotation data.
Cl
H2O
O
4
7. (9 pts) For each of the following pairs of molecules, provide the configuration of any chiral centers and then
indicate whether the two molecules within each pair are enantiomers, diastereomers, or are identical.
OH
OH
a.
and
O
O
Br
Br
CH3
b.
H
Cl
H
Br
Cl
and
CH3
H3C
Br
CH3
c.
and
8. (9 pts) The following substitution reaction begins with an enantiomerically pure starting material (i.e. only
the R isomer) which has []D = +53° and, after the reaction, the isolated product has []D = -35°. Explain
how this data helps you to decide which mechanism (SN1 or SN2) is operating here and suggest a simple
experiment that would back up your choice. Push arrows to show the mechanism and give a product.
Br
:P(CH2CH2CH2CH3)3
ether
5
9. (10 pts) The molecule below is Haterumalide ND, a potent anti-tumor drug. Identify 5 (five) chiral centers
within the compound and label them as being either the R or S configuration.
HO
H
Cl
O
CH3
OAc
O
CH3
H OH
CO2H
O
10. (10 pts) Provide a detailed mechanism for the following transformation that uses curved arrows to show the
breaking and forming of bonds. Identify each type of arrow-pushing process that you use and explain why
this bromide is the major product formed.
6
Chemistry 3719, Fall 2013
Exam 2 - Key
Student Name:
“Y” Number:
This exam is worth 100 points out of a total of 700 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam. Good Luck!
1
1. (10 pts) Draw two chair conformations for cis-1-t-butyl-4-ethylcyclohexane that are related through a ringflip. Then circle which conformation you expect to be more stable and explain why. Then do the same for
the trans isomer and, finally, indicate whether the cis or trans isomer should be more stable overall and
explain your choice.
1
2. (15 pts) Give the expected products, major and minor where applicable, in each of the following situations.
Be sure to take into account any changes in stereochemistry that may occur. If more than one set of reagents
is employed, product(s) from each step is/are required.
CH3
CH3
Br
NaCN, DMSO
CN
a.
SN 2 with inver sion
Br
KOC(CH3)3
b.
+
H
H
major
(lar ge base is used)
H3C
OH
c.
1.
SO2Cl
1.
2. NaSH, DMSO
O
2.
OTs
pyridine
SH
O
O
SN 2 with inver sion
O
CH3
I
d.
CH3OH
O
CH3
OCH3
O
CH3
OCH3
+
SN 1 - Racemix mixtur e f or med (~50:50)
OH
e.
NaNH2, DMSO
O
Br
Intr amolecular SN2
2
3. (9 pts) Provide each of the following molecules with an acceptable name. You may use either the common
or IUPAC names for substituents and be careful to include any stereochemical descriptors where needed.
Cl
a.
(2S,5S)-2-chloro-5-ethyloctane
CH3
b.
H
Br
F
H
(2S,3S)-2-bromo-3-fluoropentane
CH2CH3
c.
(R,E)-5-fluoro-6-methylhept-3-ene
F
4. (10 pts) On the axes given below, draw a complete reaction profile for the following reaction that includes
diagrams of all intermediates and transition states involved.
3
5. (9 pts) In the boxes provided, identify the type of arrow-pushing process in each step within the following
reaction mechanisms (i.e. nucleophilic attack, leaving group leaving, proton transfer, or rearrangement).
a.
Br
H Br
H
H
c.
OH
OH2
H OH2
- H2O
pr oton tr ansf er
L.G. leaves
H
H
H
O
OH
H2O
H2O
L.G. leaves
H2O
proton tr ansf er
Br
- Br
H
Nu: attack
r ear rangement
pr oton tr ansf er
b.
Br
H
proton transf er
Nu: attack
6. (9 pts) The following solvolysis conditions give two major products in equal amounts and, when measured
for the mixture, [α]D = 0. Provide the products and a mechanism for this process, as well as an explanation
for the optical rotation data.
OH
Cl
OH
H2O
+
SN1!
O
O
O
enantiomers formed in equal amounts so
optical rotations cancel and [ ]D = 0
Leaving group
leaves
Proton
transfer
H2O
H
OH2
O
H
H2O
H
+
O
Nu: attacks
O
flat carbocation that is attacked
equally from both sides
4
O
O
H
7. (9 pts) For each of the following pairs of molecules, provide the configuration of any chiral centers and then
indicate whether the two molecules within each pair are enantiomers, diastereomers, or are identical.
OH
(S)
(S)
a.
OH
(S)
(R)
and
O
Br
Br
CH3
b.
diaster eomer s
O
H
Cl
H
Br
Cl
and
H3C
(R)
(R)
CH3
enantiomer s
Br
CH3
(S, S)
c.
identical
and
8. (9 pts) The following substitution reaction begins with an enantiomerically pure starting material (i.e. only
the R isomer) which has [α]D = +53° and, after the reaction, the isolated product has [α]D = -35°. Explain
how this data helps you to decide which mechanism (SN1 or SN2) is operating here and suggest a simple
experiment that would back up your choice. Push arrows to show the mechanism and give a product.
The fact that the chiral starting material produces a chiral product is only reconcilable
with the SN2 mechanism; the SN1 mechanism would produce a racemic mixture of
products for which [α]D = 0 because the rotations of the equal amounts of the R and S
enantiomers would cancel.
A simple experiment to support the SN2 assignment would be to add more nucleophile;
the reaction would go faster if this is actually a second order reaction in which the
nucleophile is involved in achieving the transition state in the rate-determining step.
5
9. (10 pts) The molecule below is Haterumalide ND a potent anti-tumor drug. Identify 5 chiral centers within
the compound and label them as being either the R or S configuration.
10. (10 pts) Provide a detailed mechanism for the following transformation that uses curved arrows to show the
breaking and forming of bonds. Identify each type of arrow-pushing process that you use and explain why
this bromide is the major product formed.
Protonation by HBr produces an excellent leaving group which breaks away to leave a
secondary carbocation; this then undergoes alkyl rearrangement, with expansion of the
strained cyclobutyl ring, to produce a more stable cyclopentyl tertiary carbocation which is
finally trapped by the nucleophile to give the tertiary bromide.
6
Chemistry 3719, Fall 2013
Exam 3
Student Name:
“Y” Number:
This exam is worth 100 points out of a total of 700 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam. Good Luck!
1. (10 pts) Provide a detailed mechanism for the formation of the major product in the following conversion,
using curved arrows to describe the making and breaking of bonds, and then explain the regiochemical and
stereochemical outcomes in terms of the reactive intermediate(s) involved.
1
2. (15 pts) Give the expected major products in each of the following situations. Be sure to take into account
any changes in stereochemistry that may occur. If more than one set of reagents is employed, product(s)
from each step is/are required.
1. excess NaNH2
a.
2. H2O
Br Br
1. NaNH2, THF
b.
2. CH3CH2CH2Br
1. H B
c.
2. NaOH, H2O2
CH3
d.
CH3
1. CH3CO3H
2. H+/H2O
CH3
1. Br2, heat
e.
O
2. KOt-Bu, THF
2
3. (9 pts) Provide each of the following molecules with an acceptable name. You may use either the common
or IUPAC names for substituents and be careful to include any stereochemical descriptors where needed.
F
a.
b.
c.
4. (10 pts) On the axes given below, draw a complete reaction profile for the following addition reaction that
includes diagrams of all intermediates and transition states involved. Then indicate which step is ratedetermining and whether that step is unimolecular or bimolecular.
3
5. (9 pts) Provide a complete mechanism for the following conversion that features curved arrows to describe
the making and breaking of bonds. Why is a ketone formed and not an aldehyde in this reaction?
6. (9 pts) The following conditions induce a free radical halogenation process at the allylic position with only
two alkyl halide products being formed with a combined []D = 0. Give a complete mechanism for the
formation of the alkyl bromide products and an explanation for the optical rotation data.
4
7. (9 pts) For each of the following pairs of structures, circle the one that should be more stable. Then write a
few words of explanation for your choices.
CH2
CH2
a.
and
b.
and
c.
OAc
OAc
Hg
Hg
and
8. (9 pts) Give a detailed mechanism for the following ozonolysis reaction that uses curved arrows to show
the making and breaking of all bonds. What is the driving force (i.e. thermodynamic motivation) for this
kind of process that results in both carbon-carbon sigma and pi bonds being broken?
5
9. (12 pts) Provide a sequence of reagents and conditions that would allow for the following conversions.
Show the expected major products from each step of your syntheses.
?
H3C
H3C
H3C
H3C
CH3
?
10. (8 pts) Explain why the following reactions give such different outcomes in terms of the percentages of
products formed. Discuss the radicals formed and the transition states for H-abstraction in each case.
Cl2, h
+
Cl
Cl
72%
Br2, h
28%
+
Br
Br
100 %
6
0%
Chemistry 3719, Fall 2013
Exam 3 - Key
Student Name:
“Y” Number:
This exam is worth 100 points out of a total of 700 points for Chemistry 3719/3719L. You have 50 minutes to
complete the exam. Good Luck!
1. (10 pts) Provide a detailed mechanism for the formation of the major product in the following conversion,
using curved arrows to describe the making and breaking of bonds, and then explain the regiochemical and
stereochemical outcomes in terms of the reactive intermediate(s) involved.
The regiochemical outcome is a consequence of a bromine radical abstracting H on a tertiary carbon to
produce a tertiary radical (stabilized by hyperconjugation). The stereochemical outcome is the consequence
of adding a Br radical to either face of a planar (prochiral) alkene, which produces a planar (prochiral) radical
that then abstracts H from HBr. Overall two new stereocentres and 4 stereoisomers are formed.
1
2. (15 pts) Give the expected major products in each of the following situations. Be sure to take into account
any changes in stereochemistry that may occur. If more than one set of reagents is employed, product(s)
from each step is/are required.
1. excess NaNH2
a.
1.
2.
2. H2O
Br Br
1. NaNH2, THF
b.
H
1.
2.
2. CH3CH2CH2Br
1. H B
1.
B
H
2.
H
OH
c.
2. NaOH, H2O2
CH3
d.
CH3
1. CH3CO3H
(+/-)
CH3
O
CH3
1.
2. H+/H2O
(+/-)
2.
meso
CH3
1. Br2, heat
e.
O
1.
CH3
OH
OH
CH3
(+/-)
Br CH3
2.
CH3
CH2
or
2. KOt-Bu, THF
O
(+/-)
2
O
O
3. (9 pts) Provide each of the following molecules with an acceptable name. You may use either the common
or IUPAC names for substituents and be careful to include any stereochemical descriptors where needed.
F
a.
(R)-5-fluorohex-1-yne
b.
(Z)-cyclooct-1-en-3-yne
c.
(1R,2S)-1-ethynyl-2-vinylcyclohexane
4. (10 pts) On the axes given below, draw a complete reaction profile for the following addition reaction that
includes diagrams of all intermediates and transition states involved. Then indicate which step is ratedetermining and whether that step is unimolecular or bimolecular.
3
5. (9 pts) Provide a complete mechanism for the following conversion that features curved arrows to describe
the making and breaking of bonds. Why is a ketone formed and not an aldehyde in this reaction?
A ketone is formed because the first addition of H+ to the alkyne will form a
secondary-like carbocation instead of a less stable primary-like carbocation.
6. (9 pts) The following conditions induce a free radical halogenation process at the allylic position with only
two alkyl halide products being formed with a combined [α]D = 0. Give a complete mechanism for the
formation of the alkyl bromide products and an explanation for the optical rotation data.
During the first H-abstraction step a planar allylic radical is formed which then reacts with either Br2
or Br radical from either face to produce a racemic mixture of enantiomeric products. Due to the
symmetry within the molecule reaction at either C-1 or C-3 of the allylic radical will give the same
products regardless of where reaction takes place.
4
7. (9 pts) For each of the following pairs of structures, circle the one that should be more stable. Then write a
few words of explanation for your choices.
CH2
CH2
a.
and
b.
and
c.
Benzylic radical will be stabilized
by resonance delocalization
Trisubstituted alkene features three
electron-donating alkyl groups
that help stabilize sp2 carbon atoms
OAc
OAc
Hg
Hg
Mercurinium ion has all atoms with
full complement of electrons; the
carbocation has a 6-electron C atom
and
8. (9 pts) Give a detailed mechanism for the following ozonolysis reaction that uses curved arrows to show
the making and breaking of all bonds. What is the driving force (i.e. thermodynamic motivation) for this
kind of process that results in both carbon-carbon sigma and pi bonds being broken?
Ozone is a very reactive molecule that features weak O-O bonds that get the chance to break
during the ozonolysis process. In the first step the weaker O-O and C-C pi bonds are swapped for
sigma bonds to form the molozonide, and in the second step one of the weak O-O bonds is broken,
along with the C-C sigma bond. The resultant recombination produces the ozonide shown above.
5
9. (12 pts) Provide a sequence of reagents and conditions that would allow for the following conversions.
Show the expected major products from each step of your syntheses.
?
H3C
H3C
H3C
H3C
NaNH2
CH3
excess H2, Pt
H3C
CH3Br
H3C
CH3
H3C
H3C
?
H3O+ quench
Br2, RT
Br
xs. NaNH2
Br
10. (8 pts) Explain why the following reactions give such different outcomes in terms of the percentages of
products formed. Discuss the radicals formed and the transition states for H-abstraction in each case.
In both reactions there is competition between the formation of tertiary and primary radicals with the
more stable tertiary radical being favoured in each case. The difference in product distributions is
explained by the greater reactivity, and therefore lower selectivity, of the Cl radicals. The Habstraction step for chlorination is exothermic and fast, so the transition state is early and has little
radical character. For bromination the T.S. is more like the radical so the system can sense which
type of radical is formed with tertiary being greatly favoured.
6
OChem1 Practice Problems
___________________________________________________________
___________________________________________________________
Dr. Peter Norris, 2014
Dr. Peter Norris
OChem 1
Klein Chapter 1 Problems : Review of General Chemistry
1. Draw viable structures for molecules with the following molecular formulae. Remember that each atom has
a “standard” valence when forming neutral molecules, for example halogens and H are monovalent, O is
divalent, N is trivalent, and C is tetravalent. Each of the molecules has only single bonds between atoms.
2. Draw Lewis formula structures for molecules with the following molecular formulae. Show all single bonds
as single lines and any lone pairs where appropriate.
3. Draw structures for the following molecules that include any formal charges and lone pairs where needed.
Each of the molecules has either single bonds or double bonds between atoms and there may be ionic
bonds involved in some of the structures.
4. Indicate the hybridization of each of the C, N, and O atoms in the following molecules.
5. Draw a structural formula for each of the following molecules and then, using the δ+/δ- convention, label
any dipoles that are present each molecule.
1
Dr. Peter Norris
OChem 1
Klein Chapter 1 Problems : Review of Gen Chem – Answers
1. “Draw viable structures for molecules with the following molecular formulae. Remember that each atom has
a “standard” valence when forming neutral molecules, for example halogens and H are monovalent, O is
divalent, N is trivalent, and C is tetravalent. Each of the molecules has only single bonds between atoms.”
a.
CH3Cl
b.
H
H C Cl
H
e.
C2H4Cl2
C2H5F
c.
C2H3F3
H H
H C C Cl
H Cl
or
H F
H C C F
H F
or
H H
Cl C C Cl
H H
H F
F C C F
H H
d.
C3H7Br
H H
H C C OH
H H
H H H
H C C C Br
H H H
or
or
H
H
H C O C H
H
H
H H H
H C C C H
H Br H
H H
H C C F
H H
f.
C2H6O
g.
C3Br8
Br Br Br
Br C C C Br
Br Br Br
h.
C2H4BrCl
H H
H C C Br
H Cl
or
H H
Cl C C Br
H H
2. “Draw Lewis formula structures for molecules with the following molecular formulae. Show all single bonds
as single lines and any lone pairs where appropriate.”
1
Dr. Peter Norris
OChem 1
3. “Draw structures for the following molecules that include any formal charges and lone pairs where needed.
Each of the molecules has either single bonds or double bonds between atoms and there may be ionic bonds
involved in some of the structures.”
4. “Indicate the hybridization of each of the C, N, and O atoms in the following molecules.”
5. “Draw a structural formula for each of the following molecules and then, using the δ+/δ- convention, label
any dipoles that are present each molecule.”
2
Dr. Peter Norris
OChem 1
Klein Chapter 2 Problems : Molecular Representations
1. Turn each of the following “bond-line” structures into more expanded representations in which each of the
C, N, O, and H atoms are shown.
2. From Table 2.1 in the Klein text, identify all of the functional groups present in the following molecules.
3. Add any missing lone pairs to the following line structures.
4. Draw a second resonance form for each of the following structures.
1
Dr. Peter Norris
OChem 1
Klein Chapter 2 Problems : Molecular Representations – Answers
1. Turn each of the following “bond‐line” structures into more expanded representations in which each of the C, N, O, and H atoms are shown. 2. From Table 2.1 in the Klein text, identify all of the functional groups present in the following molecules. 3. Add any missing lone pairs to the following line structures. 1
Dr. Peter Norris
OChem 1
4. Draw a second resonance form for each of the following structures.
2
Dr. Peter Norris
OChem 1
Klein Chapter 3 : Acids and Bases Worksheet
Concepts
The interaction of a protic acid with a base is the first actual chemical reaction that we study in 3719. We use it to introduce
some of the fundamental concepts of mechanism, i.e. how to describe the bond-breaking and bond-forming events that
occur as a starting material (left-hand side of the equation) is converted to product (right-hand side of the equation). Since
we use acids and bases on many occasions as reagents throughout 3719 and 3720, it is important that you know what
constitutes an acid or a base and what happens when the two interact.
Definitions:
Acids donate protons (Bronsted definition) or accept electrons (Lewis definition)
Bases accept protons (Bronsted definition) or donate electrons (Lewis definition)
General Chem:
In this case HCl is the acid (proton donor), water is the base (electron donor, proton acceptor) and the green arrows show
+
the proton being transferred to generate the conjugate acid (H3O ) and the conjugate base (Cl ). The strength of the acid in
water is measured by the dissociation constant (Ka); the larger the Ka, the stronger the acid. In other words, the stronger
the acid, the more the above reaction goes to the right. Since the values of Ka can range from very large to very small, we
use the pKa scale to give manageable numbers (pKa = -log10Ka). The pKa range for acids used in Organic Chemistry are in the
range –10 (very strong acid) to +50 (very weak acid).
pKa values from class (Table 3.1 in Klein text):
HI, HBr, HCl, H2SO4
CH3CO2H
H2O, ROH
NH3
CH4
–5 to –10
4.7
16-18
38
50
extremely strong acids
weak acid
weaker acids
very weak acid
not at all acidic
For the most part in 3719 and 3720 we will not be using water as the base; rather we will use some organic or inorganic
base which has been chosen to deprotonate the acid to a particular extent. Since we know something about relative acid
strength from pKa values, we also know a lot about the relative (conjugate) base strengths:
The task in Organic Chemistry is to decide what happens in terms of the equilibrium position when a particular acid is mixed
with a particular base. If you understand this, then you can decide which acid or base to use in particular circumstances.
The problems on the next page will give you practice with these ideas.
1
Dr. Peter Norris
OChem 1
1.
For each of the following mixtures, complete the equation, then identify the acid and base on the left and the
conjugate acid and conjugate base on the right. Comparing acid and base strengths (from pKa values) decide whether
the reaction is a) likely to happen at all, b) whether equilibrium will be established, and c) if equilibrium is established
which side is favoured?
2.
The equilibrium idea means that if the reaction is reversible there will be four species in solution at one time, the acid,
the base, the conjugate acid, and the conjugate base. Sometimes this is what is required, but at other times we need to
choose bases that will completely deprotonate every molecule of acid, i.e. send the reaction completely to the right.
These bases will include CH3CH2CH2CH2Li, NaNH2, and LiN(i-Pr)2. Weaker bases will include NaOH, NaOCH3, KOtBu, and
NaOCH2CH3. For each of these bases, give the products formed when they react with H2O, then use pKa values to get an
idea of the relative base strengths of these compounds.
3.
In OChem 2 we will study reactions based on the deprotonation of ketones such as acetone, (CH3)2C=O, which has a
pKa of 19. Given the bases LiN(i-Pr)2 and NaOCH3, decide which will be useful to completely deprotonate acetone, and
which will be useful for setting up an equilibrium. Explain your choices.
4.
Give the products from the following acid-base reactions and identify the acid and base on the left side, as well as the
conjugate acid and conjugate base on the right side of the equation.
O
+
NaOH
O
+
NaNH2
OH
+
CH3Li
OH
OH
5.
For each of the reactions in question 1 and question 4, which will have an equilibrium constant (K) greater than 1, close
to 1, or less than 1? Explain your answers.
6.
Draw the structure of the conjugate base that will be formed when 1 mole of HOCH2CH2CO2H reacts with 1 mole of
CH3CH2CH2CH2Li.
7.
The careful choice of an appropriate solvent will play a major role in whether organic reactions will be successful. For
example, reagents such as CH3Li and NaNH2 will be incompatible with solvents such as water and ethanol. Why is this?
2
Dr. Peter Norris
OChem 1
Klein Chapter 3 : Acids and Bases Worksheet – Answers
1.
“For each of the following mixtures, complete the equation, then identify the acid and base on the left and the conjugate acid and conjugate base on the right. Comparing acid and base strengths (from pKa values) decide whether the reaction is a) likely to happen at all, b) whether equilibrium will be established, and c) if equilibrium is established which side is favoured?” For this type of question you have to know the approximate pKa values discussed in class and have an idea of what they mean in terms of relative acid strength and also relative base strength. a. Here we have two acids of similar strengths (1‐butanol on the left and H2O on the right) and therefore two bases of similar strengths. In this situation, the forward reaction is favoured to about the same extent as the reverse reaction. Therefore a) the reaction left to right is likely to happen, b) equilibrium will be established, and c) the equilibrium lies approximately in the middle (similar acid strengths, similar base strengths on both sides of the equation). b. In this example we have acids of very different strength, the carboxylic acid on the left (pKa~5) is very much stronger than the ammonia on the right (pKa~38) therefore the left to right reaction is very much favoured. The reverse reaction however is unlikely to occur since the base on the right is far too weak to deprotonate such a weak acid as NH3. Therefore a) the reaction left to right will happen, b) equilibrium will not be established, and c) the right‐hand side is completely favoured. c. Here we have a situation in which the reaction will go to the right. The CH3CH2CH2CH3 is such a weak acid (pKa~50) that it is impossible to deprotonate. A 28 unit pKa difference between acids means that this is a completely irreversible reaction. Therefore a) the reaction from left to right will occur to give the products shown above, b) there will be no equilibrium established, and c) the right‐hand side would be completely favoured in this case. 2.
“The equilibrium idea means that if the reaction is reversible there will be four species in solution at one time, the acid, the base, the conjugate acid, and the conjugate base. Sometimes this is what is required, but at other times we need to Dr. Peter Norris
OChem 1
choose bases that will completely deprotonate every molecule of acid, i.e. send the reaction completely to the right. These bases will include CH3CH2CH2CH2Li, NaNH2, and LiN(i‐Pr)2. Weaker bases will include NaOH, NaOCH3, KOtBu, and NaOCH2CH3. For each of these bases, give the products formed when they react with H2O, then use pKa values to get an idea of the relative base strengths of these compounds.” completely to the right
CH3CH2CH2CH3 + LiOH
+ H2O
CH3CH2CH2CH2Li
ver y str ong
base
NaNH2
+
ver y str ong
base
LiN(i-Pr)2
+
ver y str ong
base
NaOH
+
str ong
base
NaOCH3
+
str ong
base
KOt-Bu
+
str ong
base
NaOCH2CH3
str ong
base
+
acid
C.A.
pK a ~16
pK a ~50
H2O
NH3
acid
C.A.
pK a ~16
pK a ~38
H2O
HN(i-Pr)2
acid
C.A.
pK a ~16
pK a ~38
H2O
H2O
acid
C.A.
pK a ~16
pK a ~16
H2O
HOCH3
acid
C.A.
pK a ~16
pK a ~16
H2O
HOt-Bu
acid
C.A.
pK a ~16
pK a ~18
H2O
C.B.
+
C.A.
pK a ~16
pK a ~16
completely to the right
C.B.
+
NaOH
completely to the right
C.B.
+
NaOH
equilibrium, roughly
in the middle
C.B.
+
NaOH
equilibrium, roughly
in the middle
C.B.
+
HOCH2CH3 +
acid
NaOH
NaOH
equilibrium, slightly
to the right
C.B.
NaOH
equilibrium, roughly
in the middle
C.B.
Dr. Peter Norris
3.
OChem 1
“In OChem 2 we will study reactions based on the deprotonation of ketones such as acetone, (CH3)2C=O, which has a pKa of 19. Given the bases LiN(i‐Pr)2 and NaOCH3, decide which will be useful to completely deprotonate acetone, and which will be useful for setting up an equilibrium. Explain your choices.” In this question you have to set up the equation and then decide whether the base employed is indeed strong enough to completely deprotonate the acid, i.e. send the reaction completely to the right. Here (above) we have a very powerful base (very weak conjugate acid) and this reaction will proceed all the way over to the right, i.e. all of the acid molecules will be deprotonated. 4.
In this case (above) we are using a weaker base and even though the left to right reaction is possible, the right to left is also now possible. Equilibrium will be established here which will favour the side that contains the weaker conjugate base, in this case the left hand side. The main consequence of using this type of base here is that we now have some of all four species in solution at once. “Give the products from the following acid‐base reactions and identify the acid and base on the left side, as well as the conjugate acid and conjugate base on the right side of the equation.” Dr. Peter Norris
5.
6.
OChem 1
“For each of the reactions in question 1 and question 4, which will have an equilibrium constant (K) greater than 1, close to 1, or less than 1? Explain your answers.” 1a) K ~ 1 since acids and bases on each side are of similar strengths; 1b) No equilibrium since the acid and very strong base on the left will send the reaction completely to the right, K > 1; 1c) No equilibrium since the acid and very strong base on the left will send the reaction completely to the right, K > 1; 4a) K > 1 since the stronger acid and base on the left will favour the reaction to the right; 4b) No equilibrium since the reaction will go completely to the right, K > 1; 4c) No equilibrium since the reaction will go completely to the right, K > 1. “Draw the structure of the conjugate base that will be formed when 1 mole of HOCH2CH2CO2H reacts with 1 mole of CH3CH2CH2CH2Li.” O
O
HO
pK a ~16
7.
OH
+ CH3CH2CH2CH2Li
HO
OLi
+ CH3CH2CH2CH3
pK a ~5
The more acidic carboxylic acid proton (pKa ~5) will be removed before the less acidic alcohol proton (pKa ~16) “The careful choice of an appropriate solvent will play a major role in whether organic reactions will be successful. For example, reagents such as CH3Li and NaNH2 will be incompatible with solvents such as water and ethanol. Why is this?” These reagents are very powerful bases so they will be rapidly protonated by the solvents in question and destroyed: Dr. Peter Norris
OChem 1
Klein Chapter 4 Problems : Alkanes & Cycloalkanes
1. Provide accurate names for each of the following alkanes. You may use either IUPAC or trivial names for any
substituents within these molecules.
2. Draw Newman projections for each of the following situations.
a. The highest energy conformation of 3-methylnonane along the C-4 – C-5 bond axis
b. The lowest energy conformation of trans-1-isopropyl-2-propylcyclohexane along the C-1 – C-2 axis
c. The lowest energy conformation of 7-ethyl-2,3,8-trimethyldecane along the C-5 – C-6 bond axis
3. Draw appropriate diagrams for each of the following situations and explain your choices.
a. The most stable chair conformation of 1,3-di-tert-butylcylcohexane
b. The less stable chair conformation of trans-1-isopropyl-4-methylcyclohexane
c. The less stable isomer of 1,2-di-isopropylcyclobutane
4. Indicate which species/conformation is more stable in each of the following situations and give a few words
of explanation for your choices.
1
Dr. Peter Norris
OChem 1
Klein Chapter 4 Problems : Alkanes & Cycloalkanes – Answers
1. Provide accurate names for each of the following alkanes. You may use either IUPAC or trivial names for any
substituents within these molecules.
2. Draw Newman projections for each of the following situations.
a. The highest energy conformation of 3-methylnonane along the C-4 – C-5 bond axis
b. The lowest energy conformation of trans-1-isopropyl-2-propylcyclohexane along the C-1 – C-2 axis
c. The lowest energy conformation of 7-ethyl-2,3,8-trimethyldecane along the C-5 – C-6 bond axis
1
Dr. Peter Norris
OChem 1
3. Draw appropriate diagrams for each of the following situations and explain your choices.
a. The most stable chair conformation of 1,3-di-tert-butylcylcohexane
b. The less stable chair conformation of trans-1-isopropyl-4-methylcyclohexane
c. The less stable isomer of 1,2-di-isopropylcyclobutane
4. Indicate which species/conformation is more stable in each of the following situations and give a few words
of explanation for your choices.
b.
a.
CH2CH3
CH2CH3
or
or
CH(CH3)2
CH(CH3)2
Both of the large substituents will be
able to be in axial positions thereby
avoiding 1,3-diaxial problems
Having the two large groups on
opposite sides of the ring will
avoid destabilizing interactions
d.
c.
CH3
H
CH3
CH3
CH3
H
H
or
H
H
or
CH3
H
CH3
The right-hand conformation has only
one CH3-CH3 gauche interaction as
opposed to two on the left
Both of the large substituents will be
able to be as far away as possible from
each other when in the anti orientation
2
Dr. Peter Norris
OChem 1
Klein Chapter 5 Problems : Stereoisomerism
1. Identify any chiral carbons in the following molecules and, using the Cahn-Ingold-Prelog rules, label their
configuration as either R or S.
2. Within each of the following pairs of molecules, identify the relationship between them as being either
enantiomers, diastereomers, or identical.
3. Convert each of the following structures as directed.
4. Identify all the chiral carbon atoms in cholesterol (below) and label them as either the R or S configuration.
1
Dr. Peter Norris
OChem 1
Klein Chapter 5 Problems : Stereoisomerism – Answers
1. Identify any chiral carbons in the following molecules and, using the Cahn-Ingold-Prelog rules, label their
configuration as either R or S.
2. Within each of the following pairs of molecules, identify the relationship between them as being either
enantiomers, diastereomers, or identical.
3. Convert each of the following structures as directed.
1
Dr. Peter Norris
OChem 1
4. Identify all the chiral carbon atoms in cholesterol (below) and label them as either the R or S configuration.
2
Dr. Peter Norris
OChem 1
Klein Chapter 6 Problems : Reactivity & Mechanisms
1. In each of the following situations, indicate whether the reactions are favoured or disfavoured in terms of
enthalpic and entropic factors in the Gibbs free energy equation (Table 6.1 might help here).
2. Draw a mechanistic interpretation (using curved arrow(s) to show bonds forming and breaking), and then an
approximate transition state (including partial electron-densities) for each of the following events.
3. Draw curved arrows to describe each of the steps in the following reaction mechanism, and then label those
steps as being one of the four types discussed in class, i.e. nucleophilic attack, loss of a leaving group, proton
transfer, or rearrangement. Then draw a transition state for each step within the mechanism, and finally
indicate which step is rate-determining and the molecularity (unimolecular, bimolecular, etc.) of that step.
1
Dr. Peter Norris
OChem 1
Klein Chapter 6 Problems : Reactivity & Mechanisms – Answers
1. In each of the following situations, indicate whether the reactions are favoured or disfavoured in terms of
enthalpic and entropic factors in the Gibbs free energy equation (Table 6.1 might help here).
2. Draw a mechanistic interpretation (using curved arrow(s) to show bonds forming and breaking), and then an
approximate transition state (including partial electron-densities) for each of the following events.
1
Dr. Peter Norris
OChem 1
3. Draw curved arrows to describe each of the steps in the following reaction mechanism, and then label those
steps as being one of the four types discussed in class, i.e. nucleophilic attack, loss of a leaving group, proton
transfer, or rearrangement. Then draw a transition state for each step within the mechanism, and finally
indicate which step is rate-determining and the molecularity (unimolecular, bimolecular, etc.) of that step.
HCl
Cl
OH
A. proton
transfer
D. nucleophilic
attack
H Cl
C. rearrangement
OH2
B. loss of
leaving
group
H
H
H2 O
Cl
carbocation formation is rate-determining
and this step is unimolecular
Transition states:
A.
B.
+
+
OH
-
H
+
OH
Cl
C.
D.
+
+
H
+
-
H
Cl
2
Dr. Peter Norris
OChem 1
Klein Chapter 7 Problems : Substitution Reactions
1. Provide each of the following alkyl halides with acceptable names. You may use either the functional class or
substitutive nomenclature as appropriate. Be sure to assign the configurations of any chiral centers.
2. Draw detailed mechanisms for the following reactions that use “curved arrows” to show the breaking and
forming of bonds and identify the mechanism that is operating.
3. Provide the products expected to be formed under each of the following sets of conditions.
1
Dr. Peter Norris
OChem 1
Klein Chapter 7 Problems : Substitution Reactions – Answers
1. Provide each of the following alkyl halides with acceptable names. You may use either the functional class or
substitutive nomenclature as appropriate. Be sure to assign the configurations of any chiral centers.
2. Draw detailed mechanisms for the following reactions that use “curved arrows” to show the breaking and
forming of bonds and identify the mechanism that is operating.
a.
b.
H3C Br
H3C OH
I
H2O
NaCN
CN
+ HBr
DMF
SN1
stepwise via
3o cation
CN
SN2 - inversion of stereochemistry
during concerted substitution
H
H3 C O H
CH3
OH2
Br
Br
c.
d.
CH3
CH3Br
S
Cl CH3
OH
DMSO
SCH3
SN1
stepwise with
rearrangement
H
C
H
HCl
Br
Br
CH3
H
H3C H
OH2
SN2 - backside attack on simple
methyl electrophile
1
CH3
Dr. Peter Norris
OChem 1
3. Provide the products expected to be formed under each of the following sets of conditions.
2
Dr. Peter Norris
OChem 1
Klein Chapter 8 Problems : Elimination Reactions
1. Provide each of the following alkene-containing molecules with acceptable names. Be careful to assign the
configurations of any chiral centers (R or S) and double bonds (E or Z).
2. Draw detailed mechanisms for the following reactions that use “curved arrows” to show the breaking and
forming of bonds and identify the mechanism that is operating.
3. Provide the products expected to be formed under each of the following sets of conditions.
1
Dr. Peter Norris
OChem 1
Klein Chapter 8 Problems : Elimination Reactions – Answers
1. Provide each of the following alkene-containing molecules with acceptable names. Be careful to assign the
configurations of any chiral centers (R or S) and double bonds (E or Z).
2. Draw detailed mechanisms for the following reactions that use “curved arrows” to show the breaking and
forming of bonds and identify the mechanism that is operating.
a.
CH3
H3C Br
OCH3
H
+ HOCH3
+ NaBr
E2 with small base favours the
trisubstituted (Zaitsev) product
b.
H
OH
H2SO4
heat
+ H2O
E1 with acid favours
the trisubstituted
(Zaitsev) product
OH2
- H2O
H
H2O
1
Dr. Peter Norris
OChem 1
c.
Cl
KOtBu
+ HOtBu
+ KCl
THF
H
OtBu
E2 with large base favours the
less-substituted (Hofmann) product
d.
H
OH
H3PO4
+ H2O
heat
E1 with migration to
the tetrasubstituted
(Zaitsev) product
OH2
H2O
H
3o cation
2o cation
3. Provide the products expected to be formed under each of the following sets of conditions.
2
Dr. Peter Norris
OChem 1
Klein Chapter 9 Problems : Addition Reactions
1. Draw detailed mechanisms for the following reactions that use “curved arrows” to show the breaking and
forming of bonds and identify the mechanism that is operating.
2. Provide the major and minor products expected to be formed under each of the following sets of conditions.
3. Provide the reagents and conditions required to facilitate the following synthetic conversions.
1
Dr. Peter Norris
OChem 1
Klein Chapter 9 Problems : Addition Reactions – Answers
1. Draw detailed mechanisms for the following reactions that use “curved arrows” to show the breaking and
forming of bonds and identify the mechanism that is operating.
a.
dil. H2SO4
racemic
Electrophilic addition of
water with rearrangement
OH
H
H
O H
O H
H
H
2o cation
H O
H
H
o
prochiral 3 cation
b.
Br
HBr
achiral
CH3CO2H
H Br
Br
H
Electrophilic addition of HBr
(hydrohalogenation) via the
more stable tertiary cation
c.
H
H3 C
B
H3 C
1. H B
H
OH
racemic
2. NaOH,
H2O2
Hydroboration-oxidation via
concerted addition followed
by concerted rearrangement
syn add'n
H3 C
H
H3 C
B
H
O
B
OOH
H OH
H3C
H
B
O OH
1
migration with
retention
Dr. Peter Norris
OChem 1
2. Provide the major and minor products expected to be formed under each of the following sets of conditions.
3. Provide the reagents and conditions required to facilitate the following synthetic conversions.
2
Dr. Peter Norris
OChem 1
Klein Chapter 10 Problems : Alkynes
1. Draw detailed mechanisms for the following reactions that use “curved arrows” to show the breaking and
forming of bonds and identify the mechanism that is operating.
2. Provide the major and minor products expected to be formed under each of the following sets of conditions.
3. Provide complete names for the following alkyne-containing molecules, including any R/S or E/Z descriptors.
1
Dr. Peter Norris
OChem 1
Klein Chapter 10 Problems : Alkynes – Answers
1. Draw detailed mechanisms for the following reactions that use “curved arrows” to show the breaking and
forming of bonds and identify the mechanism that is operating.
a.
H
excess NaNH2
THF
Br Br
NH2
concerted "E2"
concerted "E2"
H
NH2
Br
mixture of E/Z alkenes
b.
H
1. NaNH2
2. CH3CH2Br
NH2
SN2
deprotonation
Br
acetylide anion
c.
O
H2SO4, H2O
alkyne hydrolysis
including enol-keto
tautomerism
H
Ketone
deprotonation
protonation
H2O
H
H2O
H
O
H
H
H
H
trap cation
H
O
H
H
H2O
H
O
H
H
H
Enol
deprotonation
1
O
H
H
H
protonation
H
H
Dr. Peter Norris
OChem 1
2. Provide the major and minor products expected to be formed under each of the following sets of conditions.
3. Provide complete names for the following alkyne-containing molecules, including any R/S or E/Z descriptors.
2
Dr. Peter Norris
OChem 1
Klein Chapter 11 Problems : Radical Reactions
1. Draw detailed mechanisms for the following reactions that use “curved arrows” to show the breaking and
forming of bonds and any important resonance structures. Then identify the mechanism that is operating.
2. Provide the major products expected to be formed under each of the following sets of conditions.
3. Draw all of the possible resonance structures for the following radicals.
1
Dr. Peter Norris
OChem 1
Klein Chapter 11 Problems : Radical Reactions – Answers
1. Draw detailed mechanisms for the following reactions that use “curved arrows” to show the breaking and
forming of bonds and any important resonance structures. Then identify the mechanism that is operating.
a.
H3C Br
H3 C H
Br2, h
Br
Br Br
initiation
2 Br
radical abstraction
Br Br
CH3
Br
CH3
or
termination
propagation
b.
H2C H
CH2Br
NBS, heat
O
Br
N Br
initiation
O
termination
propagation
CH2
CH2
Br Br
Br
or
CH2
CH2
delocalized benzylic radical
1
CH2
Dr. Peter Norris
OChem 1
c.
HBr, H2O2
Br
HO OH
Br
anti-Markovnikoff product
Br
OH
H
radical
addition
H abstraction
3o radical
Br
H Br
d.
H2O2, heat
OH
HO OH
O
H
initiation
propagation
etc.
propagation
OH
OH
2
Dr. Peter Norris
OChem 1
2. Provide the major products expected to be formed under each of the following sets of conditions.
3. Draw all of the possible resonance structures for the following radicals.
a.
CH2
CH2
CH2
CH2
CH2
CH2
b.
c.
d.
3
Dr. Peter Norris
OChem 1
Klein Chapter 12 Problems : Synthesis
1. Provide the major products formed from each step in the following reaction sequences. Be careful to include
any changes in stereochemistry that may occur.
2. Give a sequence of reagents that would affect the following synthetic conversions. Each problem requires at
least two synthetic steps.
3. In each of the following problems, draw a starting material that could be used as a suitable precursor in the
conversion to the given product.
1
Dr. Peter Norris
OChem 1
Klein Chapter 12 Problems : Synthesis – Answers
1. Provide the major products formed from each step in the following reaction sequences. Be careful to include
any changes in stereochemistry that may occur.
a.
CH3
1. NBS, heat
2. NaOCH3, THF
CH3
H3C Br
1.
H3 C H
H3 C H
3.
2.
4.
Br
3. HBr, H2O2
4. KOtBu, THF
racemic
Br
1.
b.
3.
2.
1. Br2, CCl4
2. excess NaNH2
Br
H
+
3. H3O (quench)
4. NaNH2
5. CH3CH2Br
3.
2.
c.
H
1. Br2, h
2. KOCH2CH3
H
Br
2.
1.
BR2
OH
H
3.
4.
3. H-BR2
4. NaOH, H2O2
E/Z mixture
racemic
d.
CH3
1. HBr
2. NaOCH3,
CH3
CH3
1.
2.
3. O3
4. Zn, H2O
OH
2.
racemic
3.
H3 C
4.
O
O
O
Br
racemic
H
H3 C
O
H
O
Give a sequence of reagents that would affect the following synthetic conversions. Each problem requires at
least two synthetic steps.
1
Dr. Peter Norris
OChem 1
3. In each of the following problems, draw a starting material that could be used as a suitable precursor in the
conversion to the given product.
2
OChem 1 Mechanism Flashcards
Dr. Peter Norris, 2013
Mechanism Basics
Chemical change involves bonds forming and breaking;
a mechanism describes those changes using curved arrows
to describe the electrons involved
There are two main types of curved arrow to describe either
2-electron or 1-electron processes
Above, the X-Y bond is forming and the Y-Z bond is breaking
There are ~100 mechanisms in OChem1 and OChem2
Ch.3 Acid-Base Reactions: Lone-Pair Donors & Acceptors
Super strong acids
acids
get
weaker
Rate-determining step is bimolecular (only one step involved)
Lone pair donor + Lone pair acceptor = Acid-Base reaction
Extremely weak acid
Not acidic at all
Acid-Base reactions are generally very fast (proton, H, is accessible)
pKa -10 to -5
pKa – 1.7
pKa ~ 5
pKa ~ 10
pKa ~ 16
pKa ~ 26
pKa ~ 36
pKa ~ 60
Acid-Base reactions appear as components of other mechanisms
HI, HCl, HNO3, H3PO4
H3O+
RCO2H
PhOH
H2O, ROH
RCCH (alkynes)
RNH2
RCH3
Ch.7 Stereochemical Change in the SN2 Reaction
MeCH(Br)Et
Rate-determining step is bimolecular (no carbocation formed)
Chiral 2°carbon with leaving group attached; strong nucleophile
+ X:
MeCH(X)Et
Proceeds with “backside attack” and “stereochemical inversion”
+ Br:
Transition state is described as being trigonal bipyramidal shape
reaction coordinate
Ch.7 Primary Alcohols (& CH3OH) with H-Cl/H-Br/H-I – SN2
Rate-determining step is bimolecular (no carbocation formed)
1°alcohol (or CH3OH) + H-X → alkyl halide = SN2 reaction
ROH
+
HX
Reaction slowed by steric crowding (CH3 > 1°> 2°> 3°)
RX
+
H 2O
Concerted process, no reactive intermediate involved
reaction coordinate
Ch.7 Stereochemical Change in the SN1 Reaction
R+ + OH2
+
X
Rate-determining step is unimolecular = CARBOCATION FORMED
3°molecule (with leaving group) + nucleophile = SN1 reaction
ROH
+
HX
Carbocation is planar so is attacked from both sides to give 2 products
ROH2
+
X
Chiral starting material gives racemic mixture of enantiomeric products
reaction coordinate
RX
+
H2O
3°alcohol + H-X → alkyl halide = SN1 reaction
RX
+
H2O
Ch.7 Reaction of a Tertiary Alcohol with H-Cl/H-Br/H-I = SN1
R+ + OH2
+
X
Rate-determining step is unimolecular = CARBOCATION FORMED
ROH
+
HX
Carbocation stabilized by hyperconjugation (3°> 2°> 1°> CH3)
ROH2
+
X
Stepwise process, reactive intermediate (carbocation) involved
reaction coordinate
H2SO4
or
H3PO4
heat
H3O+ regenerated
C
H3C
H3C
CH2
H
(+ H2O)
H O H
CH3
C
RCH2CR2OH
+
H3O+
RCH2CR2OH2
+
H2O
RCH2CR2
+
H2O
RCH=CR2
Ch.8 Reaction of 3°/2°Alcohol with H2SO4/H3PO4 – E1
H3C
H3C C O H
H3C
H OH2
H3C H
(-
H2O)
3°or 2°alcohol + H2SO4 or H3PO4 → alkene = E1 reaction
reaction coordinate
Rate-determining step is unimolecular = CARBOCATION FORMED
C
H2
Carbocation stabilized by hyperconjugation (3°> 2°> 1°> CH3)
H3C
Product distribution is based on relative alkene stability (Zaitsev rule)
H3C C O H
H3C
potential energy
B
H
+ B-H
3°, 2°, or 1°alkyl halide + base → alkene = E2 reaction
H
Ch.8 Reaction of 3°/2°/1°Alkyl Halide with Base – E2
B
Rate-determining step is bimolecular = no intermediate formed
+ X
Zaitsev outcome based on alkene stability (substitution pattern)
X
Useful, predictable process since no intermediates are formed
X
H3C
H
+
H Br
H3C
H
CH3
Br
H
H
RHC=CR2
+
HX
RH2C-CR2
+
X
RHXC-CHR2
RHC-CHR2
+
X
Ch.9 Electrophilic Addition of H-X to Alkenes
H
CH3
H
H
RH2C-CXR2
Alkene + H-X (X = Cl, Br, I) gives alkyl halide addition product(s)
H
Two-step process: slower step is carbocation formation
H3C
Br
Outcome based on carbocation stability (Markovnikoff rule)
reaction coordinate
Carbocation formed so rearrangements are a possibility
CH3
H3C
H
CH3
H3C
H
+
+
H OH2
H3C
H
H
CH3
H2O
H3 C
H
H
H
H
RHC=CR2
+
H3O+
RH(HO)C-CHR 2
RHC-CHR2
+
H2O
RH2C-C(OH)R 2
RH2C-CR2
+
H2O
Ch.9 Acid-catalyzed Hydration of Alkenes
H
H
H
H O CH
3
Alkene + dilute H2SO4 (H3O+) gives alcohol addition product(s)
HO CH
3
Three-step process, the first being slow formation of carbocation
reaction coordinate
Major product formed via more stabilized carbocation (Markovnikoff)
H
Carbocation(s) generated so rearrangements will be possible
H2 O
Overall outcome is opposite to that obtained using dilute H2SO4
Second (oxidation) step retains original C-BR2 stereochemistry
First step is concerted syn addition; no intermediate(s) formed
Alkene + H-BR2 gives addition based on sterics and electronics
Ch.9 Addition-Oxidation Hydration of Alkenes
Ch.9 Addition of Halogens to Alkenes
Similar reaction with Br2/H2O gives only anti addition of “BrOH”
Formation of the bromonium ion explains stereochemical outcome
One product only suggests a modified carbocation intermediate
Only anti product indicates that this is not a syn addition pathway
Attack from opposite
side preferred
R
R
H
H
R
C O
Ch.9 Ozonolysis of Alkenes
1. O3 in CH3OH
R
O
C
H
H
First step is concerted syn addition; no intermediate(s) formed
Remarkable process that breaks both the π and σ bonds in the alkene
2. Zn, H2O
Subsequent steps involve breaking of weak O-O bonds and the C-C bond
ketones and/or aldehydes
Malozonide product is then reduced to give the carbonyl products
alkene
Process occurs through the more stable carbocation (Markovnikoff)
Tautomerism most often then leads to the more stable ketone product
Formal product of the addition is the enol, which is often not isolated
Stepwise acid- and Lewis acid-catalyzed addition of water to an alkyne
Ch.10 Hydrolysis of Alkynes
Bromination more selective than chlorination (Br radical selective)
Selectivity observed with abstraction of H (3°> 2°> 1°C-H bond)
Non-polar mechanism with homolytic bond-breaking and forming
Alkane + Cl2/Br2 and heat/light = Radical halogenation reaction
Ch.11 Cl/Br Substitution on Alkanes – Free Radicals
No rearrangements observed with free radical intermediates here
Outcome is based on relative radical stability (Markovnikoff process)
Radical process with usual steps (initiation, propagation, termination)
Alkene + H-Br and peroxide gives alkyl halide addition product(s)
Ch.11 Radical Addition of H-Br to Alkenes