Chemistry 51B
Midterm Exam 1A
August 21, 2019
NAM E ___________________________________________________
Seat Number: ___________
Directions:
1. Place your backpack under your seat and do not open it.
2. Exams with un-signed Academic Integrity Pledges will not be graded.
3. Do your best to wait until after the exam to use the restroom.
4. No questions will be answered during the last 10 min of the exam. If you finish
during the last 5 min of the exam, stay in your seat until the end.
5. At the end of the exam, turn in your test to either Dr. K. or Leah, and show
your ID.
There is an Academic Integrity Pledge on the Score Page at the end of
the exam. Be prepared to sign this (if it is true) when you have completed
the exam.
1
Multiple Choice: Circle one letter for each question.
(3 pt. ea.)
1. Which molecule, if any, is NOT a nucleophile?
CH3
PH3
a)
b)
all are
nucleophiles
H 2O
C
HC
c)
d)
e)
2. Which is the worst nucleophile?
O
O
NH2
a)
NH2
N
H
b)
OH
c)
d)
O
e)
2. Which is the strongest base?
O
O
a)
O
O
O
S
b)
SH
OH
c)
d)
e)
4. Which molecule will undergo the fastest substitution reaction with CH3OH?
Br
Br
OH
I
a)
b)
c)
d)
1
5. Identify any and all molecule(s) below that would NOT yield the target alkyne under the
conditions shown.
Br
a)
Br
Br
c)
1. 2 NaNH2
2. H2O
Br
d) all of these will give the target alkyne
Br Br
b)
e) neither b) nor c) will give the target alkyne
6. Which molecule(s) will give the target alkene at the fastest rate?
Br
Br
Br
Br
NaOC(CH3)3
FASTEST
REACTION
TO GIVE THE
TARGET
a)
b)
c)
d)
e) two of the molecules above will give
the target molecule at equally fast rates
7. How many of the molecules below could be prepared by a Williamson ether synthesis or
similar reaction? (Meaning: treatment of an alcohol with NaH followed by exposure to an alkyl
halide.)
O
O
a) 1
b) 2
c) 3
O
d) 4
O
2
Questions 8-10 (3 pt each): Write the dominant mechanism for each reaction, selecting from
these options: SN1, SN2, E1, E2. If more than one mechanism is possible, use the reaction
conditions to decide which mechanism will be dominant. You do not need to draw the
product(s).
OH
PBr3
8.
OTs
NaOCH3
9.
Br
CH3OH
heat
10.
11. Name the molecule on the left (4 pt), and draw the molecule on the right (2 pt). Include
stereochemistry in your answers as is appropriate.
OH
methyl tert-butyl ether
3
12. Provide the missing products. (25 pt) Indicate stereochemical outcomes clearly and
completely. To do so, you may need to draw more than one product or write explanatory words
(e.g. “racemic”). Use dashes and wedges only when you intend to indicate a
particular stereochemistry.
Cl
ONa
OH
excess HI
O
OH
H2SO4, heat
1. NaH
2.
Br
OH
O
H+ catalyst
CH3OH (excess)
O
H
4
13. Provide an electron pushing mechanism for the reaction. (10 points)
H2SO4, heat
trace H2O
OCH3
+
CH3OH
14. Provide an electron pushing mechanism for the reaction. (10 points)
OH
H2SO4, heat
trace H2O
+
H 2O
15. List the reagents necessary for the transformation below as a series of numbered steps.
The synthesis can be accomplished in three or fewer steps. (6 pt)
OH
O
O
5
16. Draw a reaction coordinate diagram for the reaction below, assuming it is exothermic. Draw
structures of all reactants, products, and intermediates, and place them at reasonable relative
energy levels. Do not sketch the structures of transition states. (10 pt)
+ 2 H2O
H 2O
OH
+
H 3O
+
I
I
17. The reaction below proceeds at a faster rate than the reaction in the previous question.
Explain why this is, preferably using a partial reaction coordinate diagram. You answer should
include a few words about transition state energies. (3 pt)
(You may use the next page if you need more space.)
I
+ 2 H2O
H 2O
OH
+
H 3O
+
I
6
7
SCORE PAGE
Regarding this exam, I conducted myself in a way that was consistent with the UCI Academic
Integrity Policy in all ways.
Signature
Page
Points
Possible
Page 1 + 2
21
Page 3
15
Page 4
25
Page 5
26
Page 6
13
Total
100
Score
8