Answer Key
Exam 2 Chem 22 March 2010
-
University:
Amherst College -
Course:
CHEM 221 | Organic Chemistry I Academic year:
2010
-
Views:
22
Pages:
7
Author:
ice0ver13toy
y
Exam 2
Chem 22
March 10, 2010
page
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Name
1 (25)
2 (35)
total (200)
3 (30)
chk
4 (35)
5 (40)
6 (25)
7 (15)
No scribbling in this space, please.
.
1 (18 points) For each compound below, how many separate signals would you expect to see in a
room-temperature proton-decoupled C NMR spectrum, and how many in a H NMR spectrum?
Ph
#
13
1
C NMR signals:
# H NMR signals:
6
%
r
7
13
2. (7 points) The proton-decoupled C NMR spectrum below belongs to one of the alkynes
shown, (a) Draw an X through each alkyne that is ruled out based on the number of NMR signals.
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90
80
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20
10
(b) Circle the alkyne that you believe is most likely responsible for the spectrum. (You do not
need a table of chemical shifts.)
’
ZS .
3 (13 points) Suggest a mechanism that accounts for the following transformation. As always,
show each step clearly with curved arrows, and show all proton transfers explicitly. The *
4
indicates a radioactive C.
OCH3
NaOCH3
CH3OH
A
b'
.
( 22 points) The Friedel -Crafts alkylation below produces a mixture of products . Write a
mechanism that explains this reaction . Show each step clearly with curved arrows , and show all
proton transfers explicitly .
4
t
r .
5 (30 points) (a) We learned that nitrous acid, HONO, reacts with primary aromatic amines to
form diazonium ions. But a tertiary aromatic amine cannot form a diazonium ion. Instead, the
reaction below occurs. Write a mechanism that accounts for this reaction. Show every step
clearly.
,
N(CH )2
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(b) At first glance, it may not be obvious whether a nitroso group should be electron-donating or
electron-withdrawing. Based on the H NMR data below, which is it? Explain. Draw structures.
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6 (23 points) N-methylaniline, Ph-NHCH3, displays the following ' El-decoupled C NMR
spectra. Only the aromatic region is shown. The upper spectrum was recorded at room
temperature ; the lower at -133 °C.
(a ) Explain the difference between the two spectra in terms of the structure of the compound , ( b)
Assign the four peaks in the room temperature spectrum to the aromatic Cs of the compound.
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9 . (20 points) A compound with the formula C4H60 has the 60-MHz H NMR spectrum shown
below. The integral step heights are in mm . The compound 's IR spectrum has a broad absorption
-1
around 3400 cm 1 and a sharp peak at 2150 cm (a) Draw the structure.
,
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11 ( 15 points) Suggest a synthesis of the compound below starting with benzene .
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