BOND-DISSOCIATION ENERGIES OF THE N-H BONDS IN ANILINES AND IN THE CORRESPONDING RADICAL-ANIONS - EQUILIBRIUM ACIDITIES OF ANILINE RADICAL CATIONS

The homolytic bond dissociation energies (BDEs) for the N-H bonds in 21 anilines have been estimated by combination of the equilibrium acidities (pK(HA)) and the oxidation potentials of their conjugate anions, E(ox)(A-), in DMSO. The pK(HA) and E(ox)(A-) values for para-substituted anilinide ions have been found to be linearly correlated with Hammett sigma- constants, indicating that E(ox)(A-) values for anilinide ions are dictated largely by their basicities and are perturbed to only a minor extent by the radical stabilizing or destabilizing effects of substituents. Detailed analyses of DELTApK(HA) and DELTAE(ox)(A-) values for substituted anilines, diphenylamines, and phenols and a comparison with values for alpha-substituted acetophenones have revealed close similarities in the ways in which substituents affect BDEs. The pK(HA.+) values for 19 radical cations derived from substituted anilines were found to fall in the range of 1.2-10, and pK(HA.+) values for 14 radical cations derived from diphenylamines and related compounds fell in the range of -0.13 to +4.7. A linear correlation of the oxidation potentials of anilines vs the acidities of the corresponding radical cations was observed. The BDEs of the N-H bonds in 10 radical anions derived from anilines, diphenylamines, and related compounds were estimated by a combination of the pK(HA) values of the nitrogen acids with their reduction potentials. These estimates showed that addition of one electron weakened the N-H bonds by about 35-60 kcal/mol.