Circle one:
I wish to have my exam
put in the rack.
Printed Name
I wish to pick up
my exam.
.
(Please print clearly)
Signature
.
CHEMISTRY 262
Exam l
100 Points
February 5, 2014
6:30 – 8:30 PM
This exam has 8 problems on pages 2 through 8.
RULES
1.
2.
3.
4.
The use of a calculator and model kits are not permitted.
This exam is closed book and closed note. No aids other than writing implements
are permitted.
Answer the questions in the spaces provided on this exam.
If you wish to ask a question about procedures or about a problem on the exam,
raise your hand.
1.
6.
2.
7.
3.
8.
4.
5.
TOTAL:
/100
2
1. Predict the major product or products (be inclusive) that you would expect to be formed in
five of the following seven reactions. If you feel that no reaction will occur, then answer no
reaction. Be sure to answer only five problems. If you answer more than five, then only your
first five will be graded. (10 points/ 2 pts. each)
O
1) Me
(a)
Cl , AlCl3
2) NaBH4
NO2
1 equiv. NaOMe
Br
(b)
Br
(c)
1) Br2, FeBr3
2) Mg(0)
O
3) CO2
NO2
CO, HCl
(d)
AlCl3, CuCl
(e)
OMe
1 equiv. HNO3
H2SO4
(f)
CH3
1) 1 equiv. Br2, FeBr3
2) PhMgBr
1) HNO3, H2SO4
2) Zn(Hg), HCl
(g)
O
3)
Me
4)
Me
O
, Na2CO3
Cl
, AlCl3
Cl
3
2. Fill in the reagents needed for accomplishing two of the three following transformations.
More than one step is required. Remember that the order of the steps in a synthesis is
important. Be sure to answer only two problems. (6 points/ 3 pts. each)
NH2
(a)
Me
(b)
NH2
HO
(c)
NO2
3.
a. What is the equilibrium constant for the following reaction? (5 points)
H
H
Keq = ?
+
_
Na+
pKa = 50
_ Na+
+
H
H
H
pKa = 35
b. What does the equilibrium tell you about the cyclic anion? Why? (4 points)
4
4. In class, we talked about the 6-mercaptopurine (6-MP) pro-drug Imuran. Imuran can be
synthesized from the reaction illustrated below.
O2N
Cl
3
N
N
1
6
S
8
N
H
O2N
N
1
N
-S
+
Li
N
N
N
N
Me
N
H
N
Me
+ LiCl
N
Imuran
a. Write a “curved-arrow” mechanism for the conversion of 1 into Imuran. (5 points)
a. The reaction can also be catalyzed with acid. Starting material 1 has four nitrogen atoms.
One of them is not basic (they are numbered for your convenience). Which one and why?
You should support your answer with an appropriate drawing. (5 points)
c. The reaction above represents one of the two major mechanistic paradigms we learned for
aromatic chemistry. A representative example of the second is illustrated below. Write a
“curved arrow” mechanism for this reaction. (5 points)
SO3
H2SO4
SO3H
5
5. The hydrolysis of Imuran to 6-MP is shown below.
O2N
N
S
N
N
H
N
N
Me
OH
+
H , H2O
N
N
H
N
N
O2 N
+
N
N
N
Me
HS
a. The reaction can be monitored by IR. It forms both an alcohol and a thiol. Knowing that
sulfur has the same electronegativity as carbon, would you expect to find the OH or the
SH stretch at a higher wave number? Why? (5 points)
b. Which of the two peaks (OH or SH) would you expect to be associated with the most
intense stretch in the IR? Why? (5 points)
c. Similar trends can be seen in the carbonyl region of an IR spectrum. Order the following
four molecules from highest (1) to lowest (4) wave number for the stretch that you would
expect to see in the carbonyl region of an IR spectrum. (5 points)
O
Me
O
Me
Me
O
NMe2
Me
O
Cl
Me
OMe
d. As we mentioned above, sulfur has the same electronegativity as carbon. So where in
the order above would you place the thioester below? Why? There is a periodic table
attached to the back of the exam if you need it. Please restrict your answer to no more
than one or two sentences. (5 points)
O
Me
SMe
6
6. Mass spectrometry can also serve as an excellent way to monitor reactions.
a. For example, when we talked about IR spectroscopy we mentioned that OH stretches are
broad due to the fact that the protons involved rapidly exchange. One can follow this
exchange with the use of a mass spectrometer. Consider the equilibrium below. If you
started with a 1:1 mixture of compound 2 and 3, then how could you use mass spectrometry
to follow the formation of 4 and 5? (5 points)
O
H
O
+
MeO
D
O
O
+
MeO
3
2
D
4
H
5
b. One can also use mass spectrometry to determine the outcome of reactions like the one
illustrated below. How can you use mass spectrometry to show that the reaction forms 8 in
preference to 7? Be specific as to what you would look for. (5 points)
MgBr
O
a)
H
6
O
HO
H
b) workup
O
7
H
+
O
HO
8
7. a. Last semester, you learned about the frontier molecular orbitals involved in an SN2reaction. For the reaction shown below, please illustrate these orbitals paying particular
attention to the σ*-orbital of the Me-Br bond. (5 points)
MeO +
Me-Br
MeOMe +
Br
7
b. In class, we mentioned that this picture of the SN2-reaction ruled it out as the
mechanism for a nucleophilic aromatic substitution reaction like the one illustrated. Why?
(5 points)
Br
MeO +
OMe
+ Br
-
8. Consider the Diels-Alder reaction shown below.
O
OMe
O
MeO
+
OMe
heat
OMe
OMe
OMe
O
+
OMe
OMe
OMe
a. On the left hand side of the energy diagram below, please add the orbitals for butadiene
and ethylene. Be sure to include proper phasing, etc. (5 points)
Energy
0
O
OMe
MeO
OMe
8
b. On the right hand side of the energy diagram, readjust the energy levels of your orbitals
to account for the substituents added to the diene and the dienophile. What is the key
HOMO/LUMO interaction that will control the course of the reaction (you can just circle it
on the diagram). (5 points)
c. The reaction illustrated is sometimes referred to as an inverse electron demand Diels
Alder reaction. Can you still catalyze it with a Lewis acid? Why or why not? (5 points)
d. In the picture of the reaction above, there are two suggested products. Use a “curved
arrow” mechanism to predict which project would be the major one formed. (5 points)