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

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