Fig. 4. (A) Excitation of benzophenone to its triplet state and photolytic generation of cumyloxyl radicals from dicumylperoxide. (B) The HAT rate constants for PhSO₂H (red) and TrptSOH (black) with cumyloxyl radicals plotted as a function of medium βH2. (C) Dependence of the pseudo-first order rate on the concentration of PhSO₂H upon excitation of BP in benzene at 25 °C and non-linear fit; inset: example decay of ³BP. (D) Contribution of sulfinic acid dimerization to the observed HAT rate constant. (E) The HAT rate constants for PhSO₂H (black), TrptSO₂H (red) and TrptSOH (blue), with ³BP, plotted as a function of medium βH2 (F and G) calculated (CBS-QB3) transition state structures and associated free energy barrier, estimated rate constant and reaction free energy for HAT between a model alkoxyl radical (t-BuO˙) and PhSO₂H and t-BuSOH.