N-H BOND-DISSOCIATION ENERGIES, REDUCTION POTENTIALS AND PK(A)S OF MULTISUBSTITUTED ANILINES AND ANILINE RADICAL CATIONS

The one-electron reduction potential and the pK(a) of 10 ortho-, meta- and para-substituted aniline radical cations have been determined by means of pulse radiolysis. The N-H bond dissociation energies of the c orresponding anilines were also determined using a thermodynamic cycle . All three properties of the aniline radical cations and the correspo nding anilines were shown to be linearly dependent on the sum of the B rown substituent constants, Sigma sigma(+). A conditional scale for or tho substituents was also derived (sigma(o)(+) = 0.73 sigma(p)(+)). Th e results from this work along with previously published results have been used to derive a linear free energy relationship between one-elec tron reduction potentials of benzene radical cations and the substitue nt pattern. In addition an equation for the calculation of X-Y bond di ssociation energies of arbitrarily substituted molecules with the gene ral formula Ph-X-Y is proposed.