Correlation of Oxidation and Ionization Potentials for Azoalkanes

• Published in: Journal of organic chemistry 1997-07, Vol.62 (15), p.5128-5132
• Main Authors: Nau, Werner M, Adam, Waldemar, Klapstein, Dieter, Sahin, Coskun, Walter, Herbert
• Format: Article
• Language: English
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo970574v

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 (E p) and the vertical ionization potentials (IPv) of the azoalkanes 1−10 applies (E p = 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 NN, lengthening of the C−N bonds, and widening 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 compared with those for the corresponding bicyclic peroxide analogues.