Exam 2B - KEY - faculty.piercecollege.edu

SPRING 2012 - EXAM 2 - KEY
1. (5) (For the triene shown below, for which double bond(s) is it possible to assign E or Z
descriptors?
ANSWER: E
2. (5) In the reaction shown below, Pyridine (labeled below) can most accurately be described
as:
+
N
O
N
OH
+
O
O
H
pyridine
ANSWER: A
3. (5) What is the order of acidity of the following organic molecules? The correct answer should
list them in order of MOST acidic to LEAST acidic.
OH
OH
OH
O
OH
N
O
O
N
O
ANSWER: E
4. (15) Answer the following questions by circling either true or false. Circling both answers
results in zero points.
(a) E1 and Sn1 reactions have at least two transition states in their
TRUE
FALSE
energy profile.
TRUE
FALSE
(b) Doubling both the concentration of the nucleophile and electrophile
in an Sn1 reaction doubles the rate of reaction.
(c) Carbon skeleton rearrangements are never seen in elimination
reactions
TRUE
FALSE
(d) E2 and Sn2 reactions share a common carbocation intermediate.
TRUE
FALSE
(e) Sn2 reactions of secondary alkyl halides with NaI proceed faster in
water than in acetone.
TRUE
FALSE
5. (30) Answer the following questions about the reaction shown below.
Br
H
NaOMe
CH3
a) Write the MAJOR organic product(s) of the E2 reaction in the space above.
b) Draw the Newman projection, oriented in the only conformation that will allow the
above reaction to proceed.
Br
H
Me
H
c) Circle the answer below that accurately describes the alkene formed in (a)
neither
E-alkene
Z-alkene
2 d) Add, subtract or otherwise change no more than 3 atoms in the electrophile to create a
new molecule that will favor an SN2 reaction over an E2 reaction.
One possible answer:
Br
CH3
6. (30) Predict the product(s) of the following reactions as indicated. Be sure to include
stereochemistry when appropriate.
(a) Predict the major product(s).
KOMe
N
(b) Predict the major acid-catalyzed dehydration product(s).
or
H2SO4
H2O, heat
HO
(c) Predict the major substitution product(s).
NaCN (xs)
Cl
DMSO
Br
3 CN
CN
(d) Predict the major substitution product(s).
EtOH
O
O +
O
(solvolysis)
O
O
MsO
(e) Predict the major product(s).
Cl
EtO
Me
OTs
Cl
Me
an excess of NaOEt
acetone
Me
Me
7. (30) Fill in the missing boxes with the appropriate reactant, reagent, or product that will allow
for the reaction schemes shown below to proceed. (a) ONa
+
DMSO
Br
O
Sn2
(b) Br
KOH
OH
O
O
4 (c) NaCN
N3
CN
(1R,3R)-1-azido-3-methylcyclopentane
KBr
NaN3
N3
(1S,3R)-1-azido-3-methylcyclopentane
Br
5 8. (30 points) The following reaction proceeds via solvolysis with the product shown as one
possible product. In the box provided, write out the complete mechanism for this
transformation. Show all intermediates, all appropriate lone pairs, formal charges and
curly arrows.
Br
MeOH
solvolysis
O Me
Br
MeOH
solvolysis
O Me
Me
H
O
H
Me
6 O H
O Me