Nonadiabatic Proton/Deuteron Transfer within the Benzophenone−Triethylamine Triplet Contact Radical Ion Pair:  Exploration of the Influence of Structure upon Reaction^†

The dynamics of proton transfer within a variety of substituted benzophenone−triethylamine triplet contact radical ion pairs are examined in the solvents acetonitrile and dimethylformamide. The correlation of the proton-transfer rate constants with ΔG reveals an inverted region. The kinetic deuterium isotope effects are also examined. The solvent and isotope dependence of the transfer processes are analyzed within the context of the Lee−Hynes model for nonadiabatic proton transfer. Theoretical analysis of the experimental data suggests that the reaction path for proton/deuteron transfer involves tunneling, and the origin of the inverted region is attributed to a curved tunneling path.