Fragmentation of Substituted Acetophenone and Halobenzophenone Ketyls. Calibration of a Mechanistic Probe

Abstract

Disubstituted acetophenones, XC4H4COCH2Y, and benzophenones, XC4H4COC6H4Y, are used to measure the cleavage rate constants, kfy of a series of a-substituted acetophenone ketyls and ring-substituted benzophenone ketyls. The cleavage rate constants can be determined from the competitive rates of fragmentation, kn/kfx of a series of ketyls, [XC6H4COCH2Y],− and [XC6H4COC6H4Y]−, since the rate constants, kfx for a number of ketyl fragmentations have been electrochemically determined. Ring fragmentation is not significantly affected by substitution at the a-position of the acetophenone nor on the opposite ring of the benzophenone. The ketyls are formed by the reaction of l,3-dimethyl-2-phenylbenzimidazoline (DMBI) with the disubstituted ketones. Ketyl fragmentation can be used as a diagnostic chemical probe for reactions of ketones suspected of having ketyl intermediates. © 1991, American Chemical Society. All rights reserved.