CHE 230 - Organic Chemistry
Exam 2, March 12, 2003
Name
Student ID No.
KEY
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. 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
until 9:50 to complete this exam. There will be no extensions, so budget your time carefully.
If you wish to have your exam score posted beside your student ID number in the glass case (1st
floor, CP Building, behind CP-139) with the exam key, place an ‘X’ in this space
. If
you do not mark this space, your exam score will not be posted.
Problem
Points
1.
8
2.
10
3.
8
4.
10
5.
4
6.
9
7.
15
8.
10
9.
10
10.
6
11.
10
Total
100
Score
1
1.
(8 points) For each pair of structures below, identify them as diastereomers, enantiomers,
or identical.
SAME
DIASTEREOMERS
NH2
NH2
ENANTIOMERS
SAME
2.
(10 points) Circle the best nucleophile in each of the following pairs. Assume that the
comparison is being made in polar aprotic solvent.
a) H2O or H2S
b) NH3 or KNH2
c) NaSCH3 or HSCH3
d) NaI or NaCl
e)
or NH3
N
2
3.
(8 points) What nucleophiles would serve to effect the following conversions of 1iodopropane? Please provide a complete, neutral species (i.e. "NaBr), not "Br-").
Reagent
N3
SH
reagent
I
CN
O
4.
NaN3
NaSH
NaCN
NaOPh
(10 points) Draw each of the following compounds in the most stable chair
conformation. Be sure that each carbon with substitutents appears to be tetrahedral.
a)
CH3
tBu
H
H3C
tBu
H
H
b)
CH3 CH3
H
H3C
H
CH3
H
5.
H
(4 points) Which of the following polycyclics has a boat cyclohexane within it? (circle
all that do).
H
H
H
H
H
H
3
6.
(9 points) Draw an energy profile diagram for the reaction shown below. On your
diagram, label the transition state and the activation energy for the rate-determining step.
LiCN
CH3CH2Br
CH3CH2CN
CH3CN
Transition state
Energy
Ea
Reaction Progress
7.
(15 points) Predict the products of each reaction below. Be sure that you indicate
stereochemistry, where relevant. If you believe that no reaction will occur, write "NO
REACTION."
a)
Br
NaI, CH3CN
No Reaction
b)
NaI
Cl
I
acetone
c)
Cl
CN
NaCN
DMF
Cl
Cl
4
8.
(10 points) For each of the reactions below, determine if they proceed by a SN2 or SN1 or
mechanism.
a)
CH3NH2
Br
Br
N
S N2
b)
Br
OH
H2O, heat
S N1
S
9.
racemic
(10 points) Explain with crystal clarity why treatment of propyl alcohol with bromide ion
fails to give propyl bromide, but treatment with HBr succeeds. Do not exceed the space
provided. A sentence or two will suffice.
Na+Br-
Br
OH
HBr
Br
In the first case, hydroxide would have to be a leaving group, but it ISN'T
a leaving group in substitution rxns. In the second case, the hydroxyl gets
protonated, so the leaving group is H2O, a fine leaving group.
5
10.
(6 points) Draw a viable mechanism for the reaction below. Be sure that you use the
mechanism arrows correctly.
OTs
N(CH3)3
(CH3)3N
+ OTs
N(CH3)3
OTs
+ OTs
N
11.
(10 points) Explain why adamantyl bromide (1) fails to give the alcohol product shown,
although other tertiary bromides (like 2) react readily.
H2O
Br
OH
1
Br
H2O
OH
fast
2
Dissociation of adamantyl bromide cannot produce a planar sp2 cation, so
ionization is unfavorable. The second case does not have this restriction, so
formation of the cation intermediate proceeds normally.
END OF EXAM
6