Electrochemical Oxidation and Structural Changes of 5,6-Dihydrobenzo[ c ]cinnolines

The anodic oxidation of tetraphenylhydrazine ( 1 ) and various 5,6-dihydrobenzo[ c ]cinnoline derivatives ( 2 − 10 ) in liquid SO 2 and CH 2 Cl 2 was studied by cyclic voltammetry at different temperatures. All compounds could be oxidized to their respective dications and in some cases to their trications. The unusual results indicate a high internal reorganization energy during the first oxidation step. X-ray structure determinations and other findings reveal that the electron transfer reactions are accompanied by structural changes of the molecular framework. The mechanism of oxidation will be dicussed in terms of different variants. Digital simulations and experimental data give strong evidence for an E i E−DISP mechanism.