CHE 232 - Organic Chemistry
Exam 4, May 4, 2006
Name
KEY
Student ID No.
Before you begin this exam: First: You are allowed to have a simple model set at your seat.
Please put away all other materials. Second: Place your student identification on your desk. A
proctor will come around to check everyone’s ID. If you do not have ID, tell the proctor. Third:
Read through the entire exam. Your goal, as always, is to score as many points as possible. Do
not waste time on problems that you can’t do if there are others that look easy. Fourth: It is
critically important that your answers be written in a clear, unambiguous manner. Answers in
which your intentions are unclear will not receive credit. Fifth: READ THE
INSTRUCTIONS FOR EACH PROBLEM. You have 120 minutes to complete this exam.
There will be no extensions, so budget your time carefully.
Problem
Points
1.
6
2.
8
3.
6
4.
6
5.
5
6.
20
7.
8
8.
16
9.
15
10.
10
Total
100
Score
1
1.
(6 points) Convert the following drawing into a Fischer projection.
OH
CHO
HO
H
H
OH
HO
H
CH2OH
CHO
HO
HO OH
2.
(8 points total) a) (6 points) Convert the Fischer projection below into a zig-zag, wedgeand-dash drawing, like the one given in problem 1. The main chain is drawn for you –
simply draw in the remaining –OH groups in the correct stereochemistry.
CHO
H
OH
HO
H
H
OH
CH2OH
OH
CHO
HO
OH OH
b) (2 points) Is this compound a D-sugar or an L-sugar? A D-SUGAR
3.
(6 points) For the following structure, indicate whether it is a) an aldose or a ketose, b) a
furanose or a pyranose, and c) an α- anomer or a β-anomer (3 answers required).
HO
OH
OH
HO
O
H
OH
a) Aldose
b) Pyranose
c) β-Anomer
2
4.
(6 points) Circle the amino acids that do NOT fit the common structural motif of the
naturally occurring amino acids:
OH
O2C
H3N
CO2
CO2
NH3
H3N
CO2
H3N
CO2H
5.
H3N
CO2
H3N
CO2
H2N
(5 points) In a synthetic peptide chain composed of 10 amino acids, how many
stereoisomers are possible? Expressing the answer as an exponential is acceptable.
210
6.
(20 points, 4 pts. each) Predict the products of the reactions below. If a reaction should
produce a specific stereochemistry, be sure to indicate that stereochemistry. If you
believe that a mixture of isomers will result (like ortho and para isomers), show both. If
you believe that no reaction will take place, write “no reaction.” Do any 5 of the
following 9.
a)
NH3 Cl
O
H
1. NH3, KCN
CO2H
2. HCl, H2O, reflux
3
b)
CHO
H
OH
H
OH
CH2OH
excess
O
O
CHO
H
OAc
H
OAc
CH2OAc
O
c)
NNHPh
CHO
H
OH
HO
H
H
OH
CH2OH
excess PhNHNH2
NNHPh
HO
H
H
OH
CH2OH
d)
H
N
CO2H
H
N
H2N
DCC
O
O
N
H
O
e)
O
O
EtO
OH
1. NaOEt (1 eq.)
PhCH2Br (1 eq.)
OEt
2. LiAlH4 (excess)
3. H2O, HCl
OH
f)
O
NO2
NO2
Cl
AlCl3
O
g)
O
1. NaOEt (1 eq.)
PhCH2Br (1 eq.)
O
OEt
O
2. NaOH, H2O
3. H2O, HCl
4
h)
1. Ph3P
2. BuLi
Br
3.
O
H
i)
OH
Br
PBr3
7.
(8 points) Fill in the missing products or reagents in the synthesis of the non-natural
amino acid cyclopentylalanine, below (one product or reagent in each box).
O
O
K
N
O
EtO
OEt
O
Br
CO2Et
N
CO2Et
O
O
Br
NaOEt
O
Cl
H3N
CO2H
1. NaOH, H2O
2. HCl, H2O, reflux
CO2Et
N
CO2Et
O
5
8.
(16 points) Draw viable mechanisms for any 2 of the 4 following reactions. Do not add
any reagents that are not given in the problem. Do any 2 of the following 4.
a)
O
O
Cl
AlCl3
Cl
O
O
AlCl3
H
C O
Cl
b)
O
CH3OH, TsOH
CH3O OH
CH3OH
TsO H
O
H
O
H
O
H
OCH3
CH3OH
6
c)
HNO3
H2SO4
H
-H
H
H OSO3H
d)
H Cl
H
O
O
HCl
CH3
HO
H
O
O
OH
H
O
O
CH3
OH
CH3
HO
CH3
O
OH
H
HO
CH3
H
O H
Cl
O
7
9.
(15 points) One of the many reasons why peptides are not prepared using an acid
chloride is shown below. Upon treatment with thionyl chloride, the alanine derivative
shown cyclizes to form an oxazolidinone. The acid chloride is a likely intermediate.
H
N
O
SOCl2
N
OH
H
O
oxazolidinone
O
O
N-acetyl alanine
a) (10 points) Draw a mechanism for the conversion of the acid chloride to the
oxazolidinone. Start with the acid chloride of N-acetyl alanine.
Cl
H
N
H
N
O
Cl
H
N
O
O
O
H
Cl
O
H
O
N
O
b)
N
H
O
(5 points) Worse still, the oxazolidinone rapidly suffers racemization (shown
below). This loss of stereochemical integrity involves formation of the enolate of
the lactone, and this happens much more rapidly than with other lactones, such as
the second example below. Provide a viable, brief explanation for why formation
of the enolate is so favorable in oxazolidinone case. A sentence or two is
sufficient.
N
mild base
H
fast
O
Oxazolidinone
O
mild base
O
O
O
H
O
O
slow
O
The enolate of the oxazolidinone is aromatic, and therefore it is very
favorable to form this ion.
N
O
N
mild base
H
O
fast
N
O
O
O
O
8
10.
(10 points) Show how the target compounds below can be prepared from the list of
reagents given. You do not need to show a retrosynthetic analysis, but working backward
from the target is often very helpful. Do any one of the following three.
a)
From diethyl malonate, benzene, methanol, ethanol, and any
inorganic reagents that you may need. You don’t have to
prepare NaOEt, or other common bases.
O
O
O
O
Diethyl malonate is EtO
OEt
Making needed reagents:
PBr3
PBr3
CH3CH2OH
CH3OH
CH3CH2Br
CH3Br
CO2H 1. LiAlH4
KMnO4
CH3Br
CH2OH
2. HCl, H2O
Synthesis:
O
O
EtO
NaOEt
OEt
O
CH3CH2Br
EtO
O
1. NaOH, H2O
O
OH
2. HCl, H2O
OEt
O
CH2OH
H2SO4
(cat.)
O
b)
Ph
From benzene, ethyl acetoactetate, ethanol, methanol, and any inorganic
reagents that you may need. You don’t have to prepare NaOEt, or other
common bases.
O
O
Ethyl acetoacetate is
N
OEt
Making needed reagents (for halides see above)
NO2
HNO3
NH2
Sn, HCl
H2SO4
Synthesis:
O
NaOEt
O
OEt CH3CH2Br
Ph
O
NaOEt
O
OEt
CH3Br
O
OEt
1. NaOH, H2O
NH2
N
O
O
2. HCl, H2O
9
c)
O
O
From diethylmalonate, cyclohexene, and any inorganic reagents that you
may need. You don’t have to prepare NaOEt, or other common bases.
Note: You have stereochemistry to control in this problem.
O
O
mCPBA
EtO
EtO2C
O
OEt
CO2H
CO2Et
OH
1. NaOH, H2O
OH
2. HCl, H2O
NaOEt
(or lactone)
O
cat. H2SO4
O
10