Organic Chemistry

and the methyl protons on the carbon that is one carbon removed from the oxygen.

The chemically equivalent protons in the following compounds are designated by

the same letter:

You can tell how many sets of chemically equivalent protons a compound has from the

number of signals in its NMR spectrum.

Sometimes, two protons on the same carbon are not equivalent. For example, the

NMR spectrum of chlorocyclobutane has five signals. Even though they are bond-

ed to the same carbon, the and protons are not equivalent because they are not

in the same environment: is trans to Cl and is cis to Cl. Similarly, the and

protons are not equivalent.

PROBLEM 3

How many signals would you expect to see in the NMR spectrum of each of the

following compounds?

a. f. k.

b. g. l.

c. h. m.

d. i. n.

e. j. o.

PROBLEM 4

How could you distinguish the NMR spectra of the following compounds?

a. b. c. CH 3 OCH 2 CCH 2 OCH 3

CH 3

CH 3

CH 3 OCH 2 OCH 3 CH 3 OCH 3

1 H

CC

Cl

H

CH 3

H

CH 3 OCH 3

CC

Cl

H

Cl

H

CH 3 CH

Br

CH 2 CHCH

O

CH 3 CHCH 2 CHCH 3 NO 2

CH 3 CH 3

CH 2 “CHCl

Br

Br

CH 3 CH 2 CHCH 2 CH 3

Cl

BrCH 2 CH 2 Br

CH 3 CH 2 CH 2 CCH 3 CH 3 CH 3

O

CH 3 CH 2 CH 2 CH 3

1 H

Ha Hb Hc Hd

Ha Hb

1 H

1 H

532 CHAPTER 14 NMR Spectroscopy

3-D Molecule:

Chlorocyclobutane

CC CC

a b

a b

a c

b

a

a

a

a

a

a

b

a

c

a

c

ab

H 3 C

H 3 C

H H

H

H

H Br

H

H

H H

H H

NO 2

H

H H

H H

CH 3 OCHCl 2

two signals three signals

one signal three signals

two signals

chlorocyclobutane

Ha and Hb are not equivalent

Hc and Hd are not equivalent

Hd

Hd

Hc

Hc

H

H

b

a

He

Cl

its^1 H NMR spectrum

has five signals

three signals

abc

CH 3 CH 2 CH 2 Br

two signals

aba

CH 3 CHCH 3

one signal

aa

CH 3 OCH 3

Br

two signals

a

a

a

b

CH 3 COCH 3

CH 3

CH 3

ac b

CH 3 CH 2 OCH 3

three signals