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CHEMISTRY 262
Exam l
100 Points
February 4, 2015
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)
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)
H2N
(a)
Br
(b)
Br
NH2
(c)
SO3H
3.
a. What is the equilibrium constant for the following reaction? (5 points)
b. Would the addition of a nitro group to the N-protonated pyrrole ring as illustrated below
increase or decrease the Keq? Why? (4 points)
O2N
H
N +
H
4
4. The following Scheme shows a recent, very clever approach to the release of an alkylating
agent (2) in cancer cells that have high levels of hydrogen peroxide.
a. In the synthesis of prodrug 1, the reaction illustrated below was conducted. For this
reaction, a special ligand on boron was used to donate electron-density to the boron. This
made the desired nucleophilic displacement go better. Why? How does making the boron
more electron-rich help a reaction on the side-chain across the ring? (5 points)
b. The reaction of 1 with hydrogen peroxide generates compound 5. Suggest a curved arrow
mechanism that explains how in the presence of water 5 is converted into products 2 and
3. (5 points)
5
c. Compound 2 in the Scheme can alkylate a DNA base pairs like adenine (shown below).
One of the nitrogen atoms in adenine is a poor nucleophile and will not under alkylation
reactions. Which one and why? Support your answer with a drawing. (5 points)
d. Compound 2 might react with any of the other four nitrogens. How would you use both IR
and mass spectrometry to determine if the alkylating agent adds to the primary amine as
shown below. Be specific as to what you would look for. (10 points)
5.
a. Please write a “curved-arrow” mechanism for the following transformation. (5 points)
b. How would you monitor the progress (loss of starting material and formation of product)
of the reaction above using mass spectrometry? Be specific (5 points)
6
c. Please provide a “curved-arrow” mechanism for the following transformation. (5 points)
6.
a. Please provide energy orbital diagrams for both the cyclopropenyl radical and the
allylradical illustrated below. (10 points)
H
H
C1
H
b. Carbon one in the cyclopropenyl radical (labeled C1 in the drawing above) can be either
sp2 or sp3 hybridized. Which hybridization would be favored? Support you answer with
your orbital energy diagrams. (5 points)
7
7. For parts a-c below, rank the three molecules shown from the highest to lowest wave number
expected for the carbonyl. Assign the carbonyl with the highest wave number a value of 1
and the carbonyl with the lowest wave number a value of 3. (6 points)
O
a)
Me
O
H
Me
O
Cl
Me
O
O
O
HN
HN
OMe
HN
b)
O
O
O
c)
H2N
O2N
b. For any one of the series above, would the molecule with the lowest or the highest wave
number have the most intense IR stretch? Why? (4 points)
8. In the two reactions shown below, the second oxidation did not lead to the expected ketone.
Instead, a product was obtained that had a molecular weight of 160 rather than the 80 that
was expected. The product also contained two carbonyl stretches (one at around 1750 cm-1
and one at around1730 cm-1) and two double bonds (one of which had an intense stretch).
8
a. What product was formed in the reaction? (Hint: You may want to consider the answer to
part b below if you don’t “see” it right away.) (5 points)
b. Why? What was wrong with the second reaction that did not impact the first one? (5
points)