Steric effects in the electroreduction of 9-anthryl styryl ketone and 9,10-anthryl bis(styryl ketone)

The electrochemical behavior of 9-anthryl styryl ketone (ASK) and 9,10-anthryl bis(styryl ketone) (ABSK) in acetonitrile and N,N-dimethylformamide at a Pt electrode was investigated by cyclic and rotating ring disk electrode (RRDE) voltammetry and controlled potential coulometry. ASK is reduced in a reversible one-electron step to form the radical anion which rapidly couples (k₂=10⁵M^?1 s^?1) to form the dimeric dianion. The dimer can be reoxidized to form ASK. ABSK is reversibly reduced to the stable dianion which shows no tendency to couple. The cyclic voltammogram wave shape suggests that the styryl-keto groups in the 9-and 10-positions are non-interacting so that the reduction occurs in two steps whose standard potentials differ by the statistically predicted 36 mV.