KINETIC ISOTOPE EFFECTS FOR ELECTRON-TRANSFER PATHWAYS IN THE OXIDATIVE C-H ACTIVATION OF HYDROCARBONS

Fast hydrogen atom transfers from various methylbenzenes (ArH) to phot oactivated quinones Q show primary kinetic isotope effects k(H)/k(D) of 2.4-5.6. The quantitative effects of added inert salt on the kineti cs and on the yields of the intermediate cation radical ArH+. demonstr ate that hydrogen transfer proceeds via a two-step sequence involving an initial electron transfer to form the ion-radical pair [ArH+., Q(-. )] which subsequently undergoes proton transfer according to the elect ron-transfer mechanism in Scheme 1.