Fig. 3. (A) Photolytic generation of the 2-methyl-2-(2-naphthyl)-1-propyl radical and its use as a radical clock to obtain the rate constant for HAT from sulfenic and sulfinic acids to alkyl radicals. (B) Ratio of reduced (R′H) to rearranged and reduced (R′′H) products as a function of the concentration of TrptSO₂H (red) or PhSO₂H (black) during photocleavage of the radical precursor in THF at 25 °C. (C) Photolytic generation of cumyl radicals from dicumylketone. (D) Dependence of the pseudo-first order rate on the concentration of PhSO₂H (red) and TrptSOH (black) upon photolysis of dicumylketone in PhCl at 25 °C; inset: example decay of the cumyl radical. (E and F) Calculated (CBS-QB3) transition state structures and associated free energy barriers, estimated rate constants and reaction free energies for HAT between a model alkyl radical (t-Bu˙) and either PhSO₂H or t-BuSOH (model for TrptSOH). (G) The HAT rate constants for PhSO₂H (red) and TrptSOH (black), determined via LFP (full symbol) and radical clock (empty symbol) plotted as a function of medium βH2.