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 corresponding anilines were also determined using a thermodynamic cycle. All three properties of the aniline radical cations and the corresponding anilines were shown to be linearly dependent on the sum of the Brown substituent constants, Sigma sigma(+). A conditional scale for ortho substituents was also derived (sigma(o)(+) = 0.73 sigma(p)(+)). The results from this work along with previously published results have been used to derive a linear free energy relationship between one-electron reduction potentials of benzene radical cations and the substituent pattern. In addition an equation for the calculation of X-Y bond dissociation energies of arbitrarily substituted molecules with the general formula Ph-X-Y is proposed.