Organic Chemistry

Section 13.5 Fragmentation at Functional Groups 495

Fred Warren McLaffertywas born

in Evanston, Illinois, in 1923. He

received a B.S. and an M.S. from the

University of Nebraska, and a Ph.D.

from Cornell University in 1950. He

was a scientist at Dow Chemical

Company until he joined the faculty

at Purdue University in 1964. He has

been a professor of chemistry at

Cornell University since 1968.

the bond between the carbon and the carbon breaks homolytically and a
hydrogen atom from the carbon migrates to the oxygen atom. Again, fragmenta-
tion has occurred in a way that produces a cation with a positive charge shared by
two atoms.

PROBLEM 10

How could their mass spectra distinguish the following compounds?

PROBLEM 11

Identify the ketones that are responsible for the mass spectra shown in Figure 13.9.

CH 3 CH 2 CCH 2 CH 3

O

CH 3 CCH 2 CH 2 CH 3

O

CH 3 CCHCH 3

O

CH 3

+

m/z = 86 m/z = 58

CH 2 CCH 3

O

H 2 CCH 2 + CH 2

McLafferty

rearrangement

+

CCH 3

O

H

H 2 C

H 2 C H

g

a b

Tutorial:

Fragmentation of ketones

m/z

m/z

0 20 40 60 80 100 120

0 20 40 60 80 100 120

100

80

60

40

20

0

Relative abundance

100

80

60

40

20

0

Relative abundance

b.

43

71

86

58

a.

29

86

57

>Figure 13.9

The mass spectra for Problem 11.