Kinetic Isotope Effects for Electron-Transfer Pathways in the Oxidative C−H Activation of Hydrocarbons

Fast hydrogen atom transfers from various methylbenzenes (ArH) to photoactivated 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 kinetics and on the yields of the intermediate cation radical ArH + • demonstrate 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 electron-transfer mechanism in Scheme 1.