Organic Chemistry

PROBLEM 37

Describe the proton-coupled NMR spectrum for compounds 1, 3, and 5 in Problem 36,

showing relative values (not absolute values) of chemical shifts.

PROBLEM 38

How can 1,2-, 1,3-, and 1,4-dinitrobenzene be distinguished by

a. NMR spectroscopy? b. NMR spectroscopy?

PROBLEM-SOLVING STRATEGY

Identify the compound with molecular formula that gives the following

NMR spectrum:

First, pick out the signals that can be absolutely identified. For example, the two oxygen

atoms in the molecular formula and the carbonyl carbon signal at 166 ppm indicate that the

compound is an ester. The four signals at about 130 ppm suggest that the compound has a

benzene ring with a single substituent. (One signal is for the carbon to which the sub-

stituent is attached, one is for the ortho carbons, one is for the meta carbons, and one is for

the para carbon.) Now subtract the molecular formula of those pieces from the molecular

formula of the compound. Subtracting and from the molecular formula leaves

the molecular formula of an ethyl substituent. Therefore, we know that the com-

pound is either ethyl benzoate or phenyl propanoate.

Seeing that the methylene group is at about 60 ppm indicates that it is adjacent to an

oxygen. Thus, the compound is ethyl benzoate.

Now continue on to Problem 39.

PROBLEM 39

Identify each compound in Figure 14.35 from its molecular formula and its NMR

spectrum.

13 C

COCH 2 CH 3 CH 3 CH 2 CO

ethyl benzoate phenyl propanoate

O O

C 2 H 5 ,

C 6 H 5 CO 2

13 C

C 9 H 10 O 2

1 H 13 C

13 C

566 CHAPTER 14 NMR Spectroscopy

200 180 160 140 120 100 80 60 40 20 0

δ (ppm)

frequency