Correlation of Oxidation and Ionization Potentials for Azoalkanes

Abstract

Oxidation and ionization potentials of azoalkanes have been measured and combined with the available literature data to afford a data set of ten cyclic, bicyclic, and polycyclic derivatives with a wide structural variation. A linear correlation (r = 0.939) between the peak oxidation potentials (Ep) and the vertical ionization potentials (IPv) of the azoalkanes 1−10 applies (Ep = 0.95(IPv) − 6.4). The approximately unit slope is interpreted in terms of relatively constant differential solvation and cationic relaxation energies for the various azoalkanes. Density functional calculations (B3LYP/6-31G*) for bicyclic azoalkanes confirm that the cationic relaxation energies are relatively insensitive to molecular strain and rigidity; the latter are known to dictate their ionization potentials. The theoretical data indicate further that the preferred modes of geometry reorganization in the azoalkane radical cations are shortening of the NN, lengthening of the C−N bonds, and widening of the C−NN, but no torsion a...