ON THE HOMOCONJUGATION OF 2 ACCEPTOR GROUPS

Cyclovoltammetric investigations have been carried out on 3,3,6,6-tetr amethylcyclohexane-1,2,4,5-tetrone (4), bicyclo[3.2.2]nonane-6,7,8,9-t etrone (5), and several of their congeners, such as o-6,6,13,13-tetram ethylquinoxalino[2,3-b]phenazine (13), ro-5,5,10,10-tetramethylpyrazin o[2,3-g]quinoxaline (17), and 13-dihydro-6,13-propanoquinoxalino[2,3-b ]phenazine (20). For 5 and 20 a large difference (Delta E degrees grea ter than or equal to 400 mV) between the first and second reduction po tentials was found, The ESR results of the radical anion 20(.-) are in support of a strong homoconjugation. ESR studies of 4(.-), 13(.-), an d 17(.-) also reveal a symmetrical displacement of the unpaired electr on over both acceptor groups on the ESR time scale which, however, bas ed on the small potential difference Delta E degrees less than or equa l to 200 mV can be most likely described to a fast electron exchange.