HOMOLYTIC BOND-CLEAVAGE ENERGIES OF THE ACIDIC N-H BONDS IN DIMETHYL-SULFOXIDE SOLUTION AND PROPERTIES OF THE CORRESPONDING RADICALS AND RADICAL CATIONS

Homolytic bond dissociation energies (BDE) of various remotely-substituted and alpha-substituted aromatic amines in solution were estimated from a thermochemical cycle combining their equilibrium acidities (pK(HA)) with the appropriate electrode potential data. The radical stabilization energies (RSE) derived from the relative BDE's indicated a general trend of radical destabilization by introducing an electron-withdrawing substituent onto either the remote or the alpha positions of the donor atom. This overall radical destabilization effect of an electron-withdrawing group is rationalized and discussed in terms of the element electronegativity and of the relative significance of the radical-stabilizing delocalization effect and the radical-destabilizing inductive effect. The acidities of the corresponding radical cations were also derived and their substituent effects are discussed as well.