CORRELATION OF OXIDATION AND IONIZATION-POTENTIALS FOR AZOALKANES

Oxidation and ionization potentials of azoalkanes have been measured a nd combined with the available literature data to afford a data set of ten cyclic, bicyclic, and polycyclic derivatives with a wide structur al variation. A linear correlation (r=0.939) between the peak oxidatio n potentials (E-p) and the vertical ionization potentials (IPv) of the azoalkanes 1-10 applies (E-p=0.95(IPv)-6.4). The approximately unit s lope is interpreted in terms of relatively constant differential solva tion and cationic relaxation energies for the various azoalkanes. Dens ity functional calculations (B3LYP/6-31G) for bicyclic azoalkanes con firm that the cationic relaxation energies are relatively insensitive to molecular strain and rigidity; the latter are known to dictate thei r ionization potentials. The theoretical data indicate further that th e preferred modes of geometry reorganization in the azoalkane radical cations are shortening of the N=N, lengthening of the C-N bonds, and w idening of the C-N=N, but no torsion about the C-N=N-C dihedral angle. The experimental and theoretical data for bicyclic azoalkanes are com pared with those for the corresponding bicyclic peroxide analogues.