Effects of α-Ammonium, α-Phosphonium, and α-Sulfonium Groups on C−H Bond Dissociation Energies

C−H bond dissociation energies of α-ammonium-, α-phosphonium-, or α-sulfonium-substituted methanes and toluenes were calculated to a precision of 1−2 kcal/mol. It was found that α-ammonium, α-phosphonium, and α-sulfonium groups all destabilize a methyl radical. α-Ammonium also destabilizes a benzyl radical, whereas α-phosphonium and α-sulfonium either slightly stabilize or destabilize a benzyl radical depending on their alkylation state.