Organic Chemistry

Section 14.8 Integration of NMR Signals 539

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CH 3

CH 3

CH 3 CCH 2 Br

4

δ (ppm)

1.6

7.0

frequency

integration

line

Figure 14.7
Analysis of the integration line in the 1 HNMR spectrum of 1-bromo-2,2-dimethylpropane.

the integration steps, you can determine that the ratio of the integrals is approximately
(The measured integrals are approximate by as much as 10%
because of experimental error.) The ratios are multiplied by a number that will cause
all the numbers to be close to whole numbers—in this case, we multiply by 2—as
there can be only whole numbers of protons. That means that the ratio of protons in the
compound is which is rounded to
The integrationtells us the relativenumber of protons that give rise to each signal,
not the absolutenumber. For example, integration could not distinguish between
1,1-dichloroethane and 1,2-dichloro-2-methylpropane because both compounds
would show an integral ratio of

PROBLEM 14

How would integration distinguish the NMR spectra of the following compounds?

PROBLEM 15 SOLVED

a. Calculate the ratios of the different kinds of protons in a compound with an integral

ratio of (going from left to right across the spectrum).

b. Determine the structure of a compound that would give these relative integrals in the

observed order.

SOLUTION

a. Divide each by the smallest number:

18.4

4

=4.6

4

4

= 1

6

4

=1.5

6 : 4 : 18.4

CH 3 CCH 2 Br

CH 3

CH 3

CH 3 CCH 2 Br

Br

CH 3

CH 3 CCH 2 Br

CH 2 Br

CH 2 Br

1 H

1,1-dichloroethane

ratio of protons = 1: 3

CH 3 CH Cl

Cl

1,2-dichloro-2-methylpropane

ratio of protons 2 : 6 = 1: 3

CH 3 CCH 2 Cl

Cl

CH 3

1:3.

2 : 8.8, 2:9.

1.6 : 7.0=1 : 4.4.