Structural effects on the electrochemisty and charge distribution of mono-, di-, and tri-cyanovinyl aromatic compounds

Abstract

The effect on electrochemical behaviour and electronic charge distribution was examined for a series of 12 vinyl aromatic compounds having the following structural variations : (a) number of cyano-groups attached to the vinyl double bond, (b) substitution para to the vinyl group, and (c) separation between para-substituent and the vinyl group. The radical anion formed in the first one-electron reduction step can either accept a second electron or undergo an irreversible dimerization. Oxidation waves were seen only with those compounds having an amino nitrogen atom para to the vinyl group. Trends in half-wave potentials caused by variation in structure are correlated by means of the Hammett–Zuman and molecular orbital approaches. Due to the strong electron-withdrawing power of the cyano-substituted vinyl group, considerable intramolecular donor–acceptor interaction occurs between the ends of the molecules. This is seen in the measured molecular dipole moments and reflected in the nitrile stretching frequencies and proton chemical shifts. Finally, the efficiences for generation of charge carriers in the compounds as measured by xerographic discharge are related to their solution reduction potentials.