Answer Key
Chemistry 22 Final Exam Solutions 2009
-
University:
Amherst College -
Course:
CHEM 221 | Organic Chemistry I Academic year:
2024
-
Views:
356
Pages:
8
Author:
vingunep14
?
f
Final Exam
Name
Chem 21
Dec 18, 2009
page
1 (30)
2 (55)
total (300)
3 (40)
4 (45)
chk
5 (40)
6 (40)
7 (30)
8 (30)
Please resist the urge to write in this space.
1. (20 points) Draw the following compounds. Show stereochemistry clearly.
-
(a) ( E ,S )-2 ,3 dichloro-1-phenyl-1-pentene
(b) (R)- 1-(bromomethyl)-3-propylcyclobutene
(c) Draw the product of an SN2 reaction of
the compound in part b with CITCChNa.
.
2 (10 points) The amide below can be protonated on O or N. Draw the most stable conjugate
acid, including any important resonance structures. 3. (20 points) (a) Write the acid- base reaction of acetone (CH3 COCH3, pKa = 20) and NaH. Draw
all structures clearly, and illustrate the reaction with curved arrows.
/ O'
O'
cIt O
ch
Ke. = tO
/> ^
'
' ’*
b>
-h
0* C
c
>
Hx
v
rA ( st
c
)
^-
j> J
ref
&\>
3*
. 5. ( 13 points) Which of the diazonium ions below would lose N2 more rapidly? Briefly explain
your choice. (A clear but brief answer will likely require structures. )
®
S'
1/
^N
\
©
N$n :
d
13 tc-S^
/AjJcz U- pjao/uCJZ_
1AA lA
A
^
H i r t r c$
0
f
<3 w/
u7_
^ v/
-
z -
Cc
^
( fXhas*.
A
«
s/
.
O
(T £T T «A
S G
’
CTi
^
Ja^s
ft
-
X' v
Y'
^
S”^ x
/ArA^
**
Is
7. ( 15 points) A fledgling chemical company has hired you as a consultant to determine the
structure of an unknown hydrocarbon (“Compound -X” ), having the formula C10H16. Compound X reacts with 2 equivalents of H2 gas in the presence of a Pd catalyst to produce l -isopropyl-4methylcyclohexane. Ozonolysis of Compound -X gives the products shown below . The company
will pay you $1 ,500 (and 15 points) if you can draw the structure of the mystery hydrocarbon in
the box.
1. O3 (excess)
+
2. (CH3 )2S
4
"Compound- X "
rcM *>
d-
£
k^-c /1 rs
-e cJ- /
/ 6,
0
/r
*
u
V/ hfij
=
H2C O
rs ' V* cc*^ \r< 4- cJro*. 11
rs\
Afc. j c, 6
-
<
page 3
. 8. (13 points) When optically active ( R, R ) Irons- 1,2-dibromocyclopentane is heated in a solvent ,
the optical activity is lost as the compound racemizes, but none of the cis stereoisomer is formed.
Suggest a mechanism that accounts for these observations.
A
optically active
racemic
9. (17 points) (a) Write a mechanism for the tautomerization below. Illustrate each step clearly
with curved arrows.
CH3OCH 3OH
f)
v
—=
?
( b) In contrast to the tautomerizations that we saw in class, this one proceeds from a ketone to an
enol. Why is the enol favored in this case?
/ S GVOv*
o/
jD
(
)
10. (15 points) Draw all the stereoisomers of the following compound. Indicate which are
enantiomers and which are diastereomers.
C
/
= CH — CH
3
J. [
HO
r
L
1
j
page 4
4r 11. (25 points) Hydration of acetylenic amines works without the usual Hg2+ catalyst. Write a
complete mechanism for the acid-catalyzed hydration below. Illustrate each step clearly with
curved arrows, and show Cs and Hs explicitly don 't draw skeletal structures. Your mechanism
i.e. formation of the amide and not the
should also explain the observed regiochemistry
isomeric keto-amine, as shown.
' '
‘O'*
oI I
M
«*
H
«
not
CH3 C C- NMe2
CH3CH2
CH3
NMe2
CH2 NMe2
H2O
—
—
*
- =
1n
-
-
4
<4
c)
- c/4 = c.— / s/ djL
^/
.
5>
0'
l
-CH
-ct )
^
I
4
i
cd
c
^4 .
>S>
'C
I
o/y
.
12 (15 points) Free radical chlorination of the optically active alkane below produces a mixture
of several mono-chlorides. Draw them, showing stereochemistry clearly. Be sure you don’t draw
the same product twice. 13. ( 15 points) (a) For the following NBS bromination, draw the organic radical intermediate(s),
then draw the product(s), showing stereochemistry.
products:
Cf„ CC„ or
NBS
RO-OR
A
*
*
radical
intermediate:
Cf ~ cx
.
14 (25 points) The reaction below proceeds by a free radical chain mechanism. Photolysis of dife/Y- butylperoxide initiates the reaction. The resulting terf -butoxy radicals abstract H to produce
the chain-carrying Bu3Sn* radical , (a) Write the initiation and propagation steps of the
mechanism.
I
tBuO-OtBu
+ Bu3SnH
+ Bu3SnI
hv
—o f Jl ^
init:
•S*n /3 u*
^
r
prop:
—
in
*
:$>
h
~~ Sn /3 M
^
(b) Write two example of chain termination steps.
2
cr -
<
eJ~< •
0^0
t-
*
Si*
PY 15. (60 points) Suggest a synthetic route for carrying out each of the following transformations in
good yield . Pay attention to stereochemistry. As long as you start with the compound shown, you
can use any other organic or inorganic compounds you need.
(a)
- /3 /
\
MQ9c
HxP
( b)
O
( racemic )
fas
>
l> U ( C)
( racemic)
'OH
&
K HxP
o
o
(d )
acetylene
^
M» /
BY
h
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