FRAGMENTATION OF SUBSTITUTED ACETOPHENONE AND HALOBENZOPHENONE KETYLS - CALIBRATION OF A MECHANISTIC PROBE

Disubstituted acetophenones, XC4H4COCH2Y, and benzophenones, XC4H4COC6H4Y, are used to measure the cleavage rate constants, k(fy), of a series of alpha-substituted acetophenone ketyls and ring-substituted benzophenone ketyls. The cleavage rate constants can be determined from the competitive rates of fragmentation, k(fy)/k(fx), of a series of ketyls, [XC6H4COCH2Y].- and [XC6H4COC6H4Y].-, since the rate constants, k(fx), for a number of ketyl fragmentations have been electrochemically determined. Ring fragmentation is not significantly affected by substitution at the alpha-position of the acetophenone nor on the opposite ring of the benzophenone. The ketyls are formed by the reaction of 1,3-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.