CHEM 203
Final Exam
December 16, 2014
ANSWERS
Your name:
This a closed-notes, closed-book exam
You may use your set of molecular models
This test consists of 10 pages
Time: 2h 30 min
1.
________ / 20
2.
________ / 20
3.
________ / 30
4.
________ / 30
5.
________ / 30
6.
________ / 40
7.
________ / 40
8.
________ / 40
TOTAL
________ / 250
=
________ / 100
This exam counts for 37.5% of your CHEM 203 grade
Chem 203
final exam
p. 2 of 10
1. (20 pts.) Indicate the approximate pKa for the dissociation of the protons in boldface in the
following molecules (write your answers in the appropriate boxes):
H O-CH2-CH3
H Br
17
–8
H OH
16
CH3
H CH2 C
CH3
H CH3
50
O
H O S CF3
O
H OH2
– 11
H NH2
– 10
34
H H
H C C H
–2
25
40
2. (20 pts.) Write an accurate mechanism for the following known reactions:
1. MCPBA
2. NaN3, then
mild H3O+
3. TsCl, pyridine
H
H
4. Zn, H+
(no mech. for
this step), then
aq. NaOH
O
H
H
O
Cl S
O
N
Zn, H+
(no mech.)
N
Cl
O
N S
O
H2O–H
O
O
OH
N3 Na+
N3
N3
excess
CH3SH
SCH3
SCH3
radical
initiator
R–R
NH2
OH
O
O
b.
OTs
N H
H
H
NH
a.
2R
H–SCH3
H
OTs
OTs
N3
N3
H–SCH3
SCH3
SCH3
SCH3
SCH3
SCH3
SCH3
H–SCH3
Chem 203
final exam
p. 3 of 10
3. (30 pts) In the appropriate boxes, draw:
a. The structure of a carbocation that is stabilized by NO hyperconjugative interactions with
C–H bonds, and that will rearrange to form a new carbocation stabilized by eight
hyperconjugative interactions with C–H bonds:
CH3
CH3
CH3
CH3
C CH2
C CH2
CH3
CH3
parent carbocation
rearranged carbocation
b. The structures of two isomeric alkenes that furnish only compound A upon treatment
with O3 followed by Zn / H+ (write your answers in the appropriate boxes):
O
A
c. The structure of an alkyl halide that is likely to react with CH3ONa to give a product of
substitution, and of one that is likely to react with CH3ONa to give a product of
elimination:
undergoes substitution
undergoes elimination
I
Cl
Chem 203
final exam
p. 4 of 10
d. Accurate mechanisms for an example of E2 reaction and an example of E1 reaction:
E2
K+
O
H
anti-β-elimination
H
H
H
Br
OH + K+ + Br—
+
E1
CH3–OH
H
CH3OH
H
H
H
H
heat
Br
H
Br—
CH3OH2
+ Br—
e. The structure of an achiral molecule that is a meso form, and that of an achiral molecule
that is not a meso form:
achiral and meso
HO
H
OH
H
achiral, but not meso
HO
OH
f. Fischer projections of a D-aldonic acid and of the corresponding D-alditol:
D-aldonic acid
H
HO
H
H
D-series
COOH
OH
H
OH
OH
OH
e.g., D-gluconic acid
corresponding D-alditol
H
HO
H
H
D-series
OH
OH
H
OH
OH
OH
e.g., D-glucitol
other answers may be acceptable
Chem 203
final exam
p. 5 of 10
4. (30 pts.) Indicate:
a. the structure of the products obtained from the following reaction:
O
H
H
H
OH
OH
OH
N
C
N
C
H C N
HO
H
H
H
OH
OH
OH
H
H
H
and
OH
OH
OH
OH
b. whether sugars i.-iv. below belong to the D or the L series (check the appropriate box):
H
O
H
OH
OH
OH
HO
H
H
H
H
HO
i.
L
H
O
OH
OH
H
OH
L
H
OH
OH
H
OH
HO
H
H
HO
ii.
D
H
O
HO
H
H
iii.
D
L
OH
O
H
OH
OH
OH
iv.
D
L
D
c. the structure of the α-methyl furanoside obtained upon reaction of the D-pentose shown in
part b. with CH3OH and acid, and that of the β-methyl pyranoside obtained upon reaction
of the L-hexose shown in part b. also with CH3OH and acid:
D-α-methyl furanoside
HO
O
H
HO
L-β-methylpyranoside
H
H
HO
O
H
OCH3
OH
HO
OH
OCH3
OH
d. whether sugars i.-iv. above will react with NaBH4 to give one or two products (check the
appropriate box):
i.
1
ii.
2
1
iii.
2
1
iv.
2
1
2
Chem 203
5.
final exam
p. 6 of 10
(30 pts) Complete the following equations by indicating all the reagents, in the correct order,
that are required to achieve the stereoselective reactions shown. List the various reagents
above / below the reaction arrows.
Note: it is understood that chiral products obtained from achiral substrates will be racemic
1. TsCl, pyridine
a.
OH
2. EtLi, CuBr
OH
b.
OH
c.
d.
Br
NH2
e.
2. EtLi, CuBr
1. H2, Lindlar cat.
1. Na, NH3 (liq)
2. OsO4, then
aq. NaHSO3
2. OsO4, then
aq. NaHSO3
aq. H2SO4
NaOH, then
OH
OH
Br
1. PBr3
O
1. Na, NH3 (liq)
2. Br2
2. Br2
2. NaN3
3. Zn / H+
OH
OH
OH
OH
mild H3O+
1. H2, Lindlar cat.
1. TsCl
pyridine
OH
1. PBr3
2. NaN3
3. Zn / H+
other answers may be acceptable
Br
Br
NH2
Chem 203
final exam
p. 7 of 10
6. (40 pts.) Draw the structure of the major product expected from the following reactions
(write your answer in the boxes). If no change is predicted, answer "NO REACTION."
1.
OK
H
a.
H
Cl
2. Br2, H2O
3. NaH
O
H
1. BH3
2. H2O2,
aq. NaOH
OH
b.
3. H2CrO4,
aq. H2SO4
O
1. H2O, H2SO4
2. PCC
NO REACTION
c.
3. CH3MgBr, then
mild H3O+
1. HBr
2. Mg
3. H2C=O
O
d.
4. H2SO4, heat
5. MCPBA
1. Cl2, hv
2.
OK
CH3O
e.
3. O3, then
Zn / H+
4. NaBH4
5. NaH, CH3I
OCH3
Chem 203
final exam
p. 8 of 10
7. (40 pts.) Indicate all the reagents, catalysts, etc., in the correct order, that are necessary to
induce the transformations shown below. List such reagents above / below the reaction
arrows. NOTE: aqueous workups are understood and do not need to be shown.
O
a.
H
O
b.
1. NaBH4
2. PBr3
3. tert-BuOK
1. CH3MgBr
2. H2SO4, heat
3. H2, Pd
c.
1. NBS, hv
2. tert-BuOK
4. TsCl, pyridine
5. NaN3
3. BH3, then
H2O2, aq. NaOH
6. Zn, H
+
NH2
1. NBS, hv
2. Mg
d.
3. CO2, then mild H3O
OH
e.
OH
O
+
1. H2SO4, heat
2. Br2, CH3OH
H
SCH3
OCH3
H
3. CH3SNa
Cl
f.
1. BH3, then
H2O2, aq. NaOH
2. NaH
OH
g.
O
1. PBr3
2. tert-BuOK
OH
3. BH3, then H2O2, aq. NaOH
h.
OH
1. H2SO4, heat
+
2. O3, then H2O2, H
3. NaH, CH3I
O
OCH3
other answers may be acceptable
Chem 203
final exam
p. 9 of 10
8. (40 pts.) Propose a good synthesis of the molecules shown below using only methanol,
acetylene and ethylene oxide (see below) as the sources of carbon atoms. Intermediates /
products obtained during an earlier sequence may be employed in a subsequent procedure.
Assume the availability of all necessary reagents (such as bases, acids, BH3, Mg, TsCl, PCC,
PBr3, MCPBA, etc.).
methanol: CH3OH
acetylene: H C C H
ethylene oxide:
O
H2C CH2
Important:
i. Aqueous workups at the end of each reaction are understood and need not to be shown.
ii. It is not necessary to write mechanisms.
a.
O
OH
PCC
H2SO4
H2
H2O
Lindlar
HI
CH3I
CH3OH
NaNH2
H2
Lindlar
H C C H
Na+
Na+
BH3, then
PBr3
OH
Br
H2O2, aq.
NaOH
O
OH
b.
OCH3
OH
H2CrO4
aq. H2SO4
Br2
part a.
CH3OH
BH3, then
H2O2, aq.
NaOH
OCH3
Br
OCH3
Na+
part a.
OCH3
H2
Lindlar
OCH3
Chem 203
c.
final exam
O
OsO4
OH
+
OH
– H2O
H2SO4
part a.
O
cat. H2SO4
O
p. 10 of 10
then aq.
NaHSO3
PCC
OH
Na+
H2O
I
part a.
H2
H C C H
OH
d.
OH
OH
Lindlar
HI
CH2=CH2
OsO4
OH
then aq.
NaHSO3
OH
H2
Lindlar
O
NaNH2
part a.
Na+
part c.
other answers may be acceptable
Happy Holidays!
H2
Lindlar