Equilibrium acidities and homolytic bond dissociation enthalpies of the acidic C-H bonds in As-substituted triphenylarsonium and related cations

The acidifying effects of an alpha-triphenylphosphonium family are found to be around 9-20 pK units stronger than related alpha-trimethylammonium on adjacent C-H bonds. The effects of alpha-triphenylarsoinium groups on the equilibrium acidity and the bond dissociation enthalpies (BDEs) of adjacent acidic C-H bonds have been studied. Acidifying effects were found to be 13-20 pK units and were due to the combined Coulombic and polarizable interaction on the ylide anions. The BDEs show that alpha-triphenylarsonium addition decreases adjacent radical stabilities by 2-5 kcal/mol.