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Chapter 14 467
Copyright © 2017 Pearson Education, Inc.
29.
a.
CH
3
OCH
2
CH
2
OCH
3
b.
There are three possibilities:
c.
HC
CH
O
O
CH
3
CCH
2
CH
2
CCH
3
O O
CH
3
OCH
2
C CCH
2
OCH
3
O
O CH
3
CH
3
30.
There is no coupling between
H
a
and
H
c
because they are separated by four
s
bonds. (We will see in
Section 14.17 that unless the sample is pure and dry, a proton bonded to an oxygen is not split and does not
split other protons.)
There is no coupling between
H
b
and
H
c
because they are separated by five
s
bonds.
31.
The two singlets in the
1
H
NMR spectrum that each integrate to 3 protons suggest two methyl groups, one
of which is adjacent to an oxygen. That the benzene ring protons (
6.7
-
7.1
ppm) consist of two doublets
(each integrating to two hydrogens) indicates a 1,4-disubstituted benzene ring. The IR spectrum also indi-
cates a benzene ring (1600 and
1500 cm
-
1
) with hydrogens bonded to
sp
2
carbons and no carbonyl group.
The absorption bands in the 1250–
1000 cm
-
1
region suggest that there are two C—O single bonds, one
with no double-bond character and one with some double-bond character.
CH
3
O
CH
3
32.
a.
J
bc
J
bc
J
ba
b.
J
ba
J
bc
J
bc
33.
a. A
b. B
and
D
34.
Solved in the text.
35.
CH
3
CCH
3
Br
Br
a a
b a b
a b c
a d b
BrCH
2
CH
2
CH
2
Br
CH
3
CH
2
CHBr
Br
CH
3
CHCH
2
Br
Br
c
one signal
a singlet
two signals
a quintet (a) and
a triplet (b)
three signals
two triplets (a and c)
and a multiplet (b)
four signals
three doublets
(a, b, c) and a
multiplet (d)
36.
Solved in the text.
37.
The OH proton of a carboxylic acid is more deshielded than the OH proton of an alcohol as a result of
electron delocalization that decreases the electron density around the OH proton. In addition, the extent
of hydrogen bonding affects the chemical shift of a proton bonded to an oxygen. Carboxylic acids exist as
tightly hydrogen-bonded dimers (see page 693 in the text); this strongly deshields the OH proton.
R O
versus
H
C
O
R O H
C
O
−
R O H
+