Kinetic isotope effect in the transfer of a hydrogen atom from a ketyl radical to an azomethine dye

Abstract

1. The kinetic isotope effect in the transfer of a hydrogen atom from a ketyl radical to an azomethine dye in alcohol solvents reaches 4.2, which points to a considerable weakening of the O-H bond of the ketyl radical in the transition state. The kinetic isotope effect is reduced when the Hammett σ-constant of the substituent on the ketyl radical decreases and is almost independent of the structure of the dye. 2. The kinetic isotope effect in toluene and in water is considerably lower than in alcohols (1.6–1.7) which is evidence of the asymmetry and nonlinearity of the transition state in the hydrogen transfer reaction.