[2.2]PARACYCLOPHANE-4,7,12,15-TETRONE, [2.2](1,4)NAPHTHALENOPHANE-4,7,14,17-TETRONE, AND 1,4,8,11-PENTACENETETRONE RADICAL-ANIONS - A COMPARATIVE ESR STUDY

Three types of tetrone radical anions in which two 1,4-benzoquinone un its are connected by ethano (1(.-), 2(.-)), [2.2]paracyclophane (3(.-) , 4(.-)), and anthracene bridges (5(.-), 6(.-)) have been studied by E SR and ENDOR spectroscopy. The displacement of the unpaired electron o ver the two pi moieties in the [2.2]cyclophane radical anions 1(.-)-4( .-) and the marked difference between the first and second reduction p otentials, Delta E = \E-2(0) -(0)(1)\ greater than or equal to 0.20 V, are evidence for a substantial intramolecular electronic interaction between the two electrophores. Similar Delta E data for the syn- (3) a nd anti-naphthalenopha nes (4) indicate that most of the intramolecula r electronic interaction takes place through the [2.2]paracyclophane b ridge. When ion pairing is inhibited by complexation of the cation, th e unpaired electron in 5(.-) and 6(.-) is also delocalized over the wh ole pentacenetetrone system at temperatures as low as 160 K.