Download 1 1. (20 pts.) Draw the major product of each of the following

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1. (20 pts.) Draw the major product of each of the following reactions. Do not draw
mechanisms! Assume aqueous workup in all cases (that is, draw neutral products).
(a)
O
OH
Et
H
EtMgBr
H
(b)
O
N
OH
HONH2
(c)
Ph
HO
O
Ph
OH
O
cat. H2SO4
remove H2O
O
(d)
CH3
Ph
O
Ph3P
CH3
CH3
Ph
CH3
2
2. (20 pts.) Design a synthesis of the ketone below. All of the C atoms in the product
must be derived from one or both of the two starting materials shown, but you may
use any other reagents to accomplish the necessary transformations. Your synthesis
will require more than two steps. Show each intermediate compound and all
reagents you will need for each step. (Don’t panic if you can’t remember the
reagents for a particular step; partial credit will be given.) Do not show mechanisms.
O
OH
and
Retrosynthesis:
O
OH
O
and
BrMg
OH
Br
Forward:
OH
Br
PCC
Mg
O
OH
MgBr
PCC
O
Br
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3. (20 pts.) The following reaction is a model for the hydrolysis of sucrose to
fructose and glucose. Draw a reasonable mechanism for it.
HO
HO
O
HO
H2O
MeO
OH
HO
O
cat. H+
OH
HO
methyl fructofuranoside
HO
OH
OH
fructose
HO
HO
O
O
O
H+
MeO
MeO
OH
HO
H HO
OH
HO
HO
O
OH
HO
HO
OH
OH
OH
HO
HO
HO
OH
HO
HO
HO
H
OH
O
OH
H2O
OH
H
O
~H+
H2O
HO
OH
OH
O
OH
HO
OH
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4. (5 pts. each, 20 pts. total.) Your summer job is to clean up an organic chemistry
laboratory after a flood has partially destroyed the labels on many of the bottles. In
each problem below, choose a method for distinguishing the two possibilities by MS,
IR, 1H NMR, 13C NMR, or optical activity, and precisely describe one difference that
you can expect to see in the spectra of the two compounds that will allow you to
identify the sample unambiguously. You may use each method no more than twice
in this problem!
(a) Bottle 1 contains one of the following:
H3C
O
CH3
H3C
O
CH3
Method for distinguishing: 1H NMR or 13C NMR
Difference: Compound on left shows four resonances; compound on right shows
two.
(b) Bottle 2 contains one of the following:
O
H3C
O
CH3
Method for distinguishing: 1H NMR or 13C NMR or IR
Difference:
IR: Compound on right shows absorbance at about 1710 cm–1; compound on left
shows much higher energy absorbance.
1H NMR: compound on left shows two singlets in 2:3 ratio; compound on right
shows three multiplets in 2:2:1 ratio.
13C NMR (proton-coupled): compound on left shows two singlets, a triplet, and a
quartet; compound on right shows one singlet and three triplets.
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(c) Bottle 3 contains one of the following:
O
NH
N OH
Method for distinguishing: IR or NMR
Difference:
IR: Compound on left shows absorbance around 3300 cm–1; one on right shows
about 3500 cm–1.
NMR (1H or 13C): Compound on left shows two downfield absorbances; one on right
shows one upfield and one downfield.
(d) Bottle 4 contains one of the following:
CH3
Method for distinguishing: 1H or 13C NMR
Difference:
1H
NMR: Compound on left shows two resonances in alkene region; one on right
shows three. Upfield resonance for compound on left integrates to 3H; one on right
integrates to 2H.
13C NMR (proton-coupled): Compound on left shows upfield quartet; one on right
shows upfield triplet.
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5. (20 pts. total) Draw in all of the H atoms in the following compound.
b
b
H
H
c
H
a
d
H
a
H
H
H
a
e
c
H
OCH3
d
H
(a) (5 pts.) Label equivalent H’s with the same letter and inequivalent H’s with
different letters, as we did in class.
(b) (15 pts.) Predict the 1H NMR spectrum of the compound, indicating the approximate chemical shift, integration, and multiplicity for each resonance that you expect
to see. You can find a table of 1H NMR chemical shifts at the front of this exam.
Type of H
δ (in ppm)
Integration
Multiplicity
a
1.1
3
t
b
2.0
2
q
c
7.2
2
d
d
6.8
2
d
e
3.8
3
s
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1. (5 pts. each, 25 pts. total) Draw the major product of each of the following
reactions. Assume aqueous workup in all cases (that is, draw neutral products). Do
not draw mechanisms!
(a)
SH
S
Br
NaH
(b)
O
O
LDA; then CH3CH2CH2I
CH3
(c)
O
O
Ph
O
H
Ph
NaOEt
(d)
O
O
O
Ph
Ph
cat. NaOEt
O
O
O
(e)
O
OH
PhMgBr
Ph
2
2. (15 pts. each, 30 pts. total) Design syntheses of the two compounds below from
the indicated starting materials. Both syntheses will require two or more steps.
Show each intermediate compound and all reagents you will need for each step.
(Don’t panic if you can’t remember the reagents for a particular step; partial credit
will be given.) Do not show mechanisms.
(a)
two alcohols
O
Retro:
O
Br
+
HO
O
OH
+
Br
or
Second one is much better because it involves a 1° alkyl halide (loves to do SN2) rather
than a 2° alkyl halide (prefers to do E2 with alkoxides)
Forward:
OH
HO
PBr3
Br
O
NaH
3
(b)
O
five-carbon starting materials
Retro:
H H
O
H
O
H H
aldol
H
H
H
H
H
O
alkylation
O
H H
H
Br
H
Forward:
H H
O
H
LDA
O
H H
H
Br
H
H
H
H
NaOEt
(or LDA, then NaOEt)
O
H H
H
Doing the two steps in the other order is fine.
O
H
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3. (25 pts. total) Draw reasonable mechanisms for each of the following reactions.
(a) (10 pts.)
O
H
OH
O
cat. H +
H
O
H
O
H
OH
OH
OH
H
H
+
H
OH
H
H+
H
H
O
H
H
O
H
O
H
H
O
H
H
O
H
H
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(b) (15 pts.)
O
O
CH3
CH3
NaOEt
O
H
O
O
H
O
CH3
O
H
H
O
CH3
CH3
–
OEt
O
H
O
EtO
O
H
O
H
H
O
CH3
OH H
H
O
O
O
H
EtO H
O
CH3
OH
H
H
H
O
CH3
O
O
H
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4. (4 pts. each, 20 pts. total) Undergraduate research assistant Bartholomew Humdinger wants to carry out each of the following reactions in the laboratory. Explain
to him why each reaction WILL NOT WORK AS WRITTEN. (Bartholomew has a
short attention span, so please restrict your answers to one or two grammatically
correct sentences. Please note that, “Because you can’t,” and “Because it won’t
happen,” are not acceptable answers.)
(a)
ONa
Br
O
3° alkyl halides don’t undergo SN2 reactions because of steric hindrance. Instead,
elimination will occur.
(b)
O
O
Br
NaOEt
When a weak base is used in ketone alkylations, multiple alkylations occur because
the product is deprotonated as often as the starting material.
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(c)
O
O
LDA; then CH3CH2CH2I
Ph
H
Ph
H
CH3
Aldehydes can’t be deprotonated with LDA and then alkylated because they undergo
aldol reactions faster than they are deprotonated.
(d)
S
OH
S
Alcohols are not electrophilic under basic conditions, so no reaction will occur.
(e)
O
O
O
Ph
OH
Ph
cat. NaOEt
When aldol reactions are carried out with a weak base, dehydration occurs and an
enone, not a β-hydroxyketone, is obtained. The β-hydroxyketone is obtained only
when a strong base like LDA is used.