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Final Exam 2001 KEY
1
1. Draw a sawhorse representation of the most stable conformation of the C2 –
C3 bond of (3R)-2,3,5-trimethylhexane. Why is it so stable?
H3 C
The hydrogen on C2 is gauche to the large
groups on C3, minimizing gauche interactions.
CH2 CH(CH 3 )2
H3 C
H
H
CH3
2. Indicate, on the lines beside each arrow, the hybridization of the carbon
atoms indicated in the molecule below:
sp3
sp2
C
OH
sp
sp3
3. Draw the compound below in its most stable conformation
Cl
CH3
Cl
Final Exam 2001 KEY
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4. Give each compound shown below its IUPAC (systematic) name.
Cl
Cl
A.
(3E, 5Z, 7R)-1,7-dichloro-2-methyl-3,5-nonadiene
B.
HO
(1R, 3R, 5’E)-3-(5-methyl-5-octenyl)cyclopentanol
C.
OH
(S)-3-methyl-2,4-cyclohexadienol
OH
D.
(R)-1-(4-cycloheptenyl)-2-propanol
E.
NH 2
NH 2
(2E, 4R)-2-hexene-1,4-diamine
Final Exam 2001 KEY
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5. Draw the major products of the following:
A. Propene + HBr/ROOR
Br
B. cis-2-butene + Br2/THF
+ mirror
Br
Br
Br
C.
+ HBr (+ FeSO 4)
D.
+
CH3
Br
HBr (+ ROOR)
HO
E.
(1) Hg(OAc)2/H2O
+
(2) NaBH4
+ mirror
Final Exam 2001 KEY
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6. What is the relationship between the following pairs of molecules?
CH3
H
H
A.
Cl
H
CH3
Cl
CH3 CH2
H
Cl
Cl
H
Cl
CH2 CH3
CH3
CH3
DIASTEREOMERS
CH3
H
OH
H
B.
CH3
SAME
H
OH
Cl
CH2 CH3
CH3
C.
OH
H
CH3
CH3
H
OH
ENANTIOMERS
Final Exam 2001 KEY
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7. Show how to accomplish the following transformations. (That means draw
the starting material, then show the reagents and the order in which they are
added, finally draw the product).
A. Convert 3,3-dimethyl-1-butene to 3,3-dimethyl-1-butanol
(1 pt for separate additions, (1) & (2)
(1) BH3 / THF (1 pt)
OH
-
(1 pt)
(2) H2 O2 , OH , H2 O (1 pt)
(1 pt)
B. Convert 3,3-dimethyl-1-butene to 2,3-dimethyl-2-butanol
+
H 3 O / H2 O
(3 pts)
OH
(1 pt)
(1 pt)
C. Convert 3,3-dimethyl-1-butene to 3,3-dimethyl-2-butanol
1 pt for separate additions
OH
(1) Hg(OAc) / H2 O (1 pts)
(2) NaBH4 (1 pt)
(1 pt)
(1 pt)
Final Exam 2001 KEY
6
Show how to prepare the following target molecules completely from 1butyne: (You do NOT have to repeat a synthesis, so if you use a compound
later that you prepared earlier, you only have to write the compound and "see
8 C" or the like as the second synthesis)
8.
A. butanal (an aldehyde)
1 pt for separate additions
(1) (siamyl)2 BH, THF (2 pts)
-
(2) OH , H2 O2 , H2 O (1 pt)
B. 2-butanone (a ketone)
2 pts
O
2 pts
H2 SO 4 , H2 O, HgSO4
O
C. (Z)-3-octene
H
(2 pt)
Na, NH3 (liq)
or
Lindlar's/H2
(2 pts)
HBr
(2 pts)
NaNH 2
Br
ROOR
TARGET
Retrosynthetic arrows are OK too:
(2 pts)
mix
(2 pts)
Lindlar's/H2
means "can be made from")
D. racemic (3R,4S)- and (3S,4R)-3,4-dibromooctane
(3 pts)
Na, NH3 (liq)
(from 8c)
(2 pts)
(2 pts)
Br2
Final Exam 2001 KEY
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9. Name the following molecule, then suggest the reactants that could have formed it in
a Diels-Alder reaction:
Cl
Cl
A. Name:
(1S,2R,3R,4R,5S,6R)-3,4-dichlorotricyclo[4.2.1.02,5]non-7-ene
B. Reactants:
Cl
+
Cl
10. Put the following nucleophiles in order of INCREASING nucleophilicity in
water (weakest first):
Acetate anion, ethyl alcohol, ethyl thiolate anion, water, phenolate anion
Water, ethyl alcohol , Acetate anion, phenolate anion, ethyl thiolate anion
11. How, with a 2° alkyl bromide, could you maximize the chances of the
reaction with a nucleophile going through the SN2 route?
Low polarity solvent, high concentration of nucleophile
Final Exam 2001 KEY
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12. Why does iodide ion make both a good leaving group and a good nucleophile
in water?
It’s a good leaving group because it’s a very weak acid (pKa of HI is –10). It’s a good
nucleophile in water because it is not solvated much.
13. When (R)-3-methyl-3-bromohexane is treated with iodide ion in a relatively
non-polar solvent, the product is only partially racemized. Explain first
what one should expect here, and then suggest a reason for this observation.
One would expect complete racemization since the carbocation formed is planar.
The bromide ion must not have left the carbocation completely, but must be hanging
around in an intimate ion pair or a solvent-separated ion pair with the carbocation.
Final Exam 2001 KEY
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14. How does one assure monobromination in the radical substitution reaction?
Use a vast excess of the alkane substrate
15. Draw the major product of each below and suggest the route taken (i.e., SN1,
SN2, etc.). Assume high concentrations of reagents listed.
A) (R)-2-bromobutane + CH3COO– (water/methanol) ROUTE: SN2
O
O
B) (R)-2-bromobutane + OH– (aq)
ROUTE:
SN2
OH
C) 2-methyl-2-bromobutane + potassium t-butoxide
D) 2-methyl-2-bromobutane + sodium ethoxide
E) 1-bromopropane + sodium methoxide
ROUTE:
ROUTE:
ROUTE:
E2
E2
SN2
O
F)
(R)-2-bromopentane + a 50-50 mixture of NaF and NaCl in DMSO.
ROUTE:
SN2
F
Final Exam 2001 KEY
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16. Suggest ways to synthesize the following compounds from butane:
A.
C N
Br
Br2
-
t BuO
-
HBr
∆
ROOR
O
B.
-
Br
OCH 3
#
from A.
C. racemic
O
-
Br
from A
OCH 3
or
solvolysis in CH3 OH
Br
CN
-
#