The phenylcyclooctatetraene anion radical and dianion: An intramolecular charge and spin distribution isotope effect

Article abstract of DOI:10.1021/ja00028a002

EPR studies on the anion radicals and ¹³C NMR studies of the dianions of phenylcyclooctatetraene ([6]-[8]), phenylcyclooctatetraene-d₇, and phenyl-d₅-cyclooctatetraene show that deuteriation of the cyclooctatetraenyl moiety perturbs and phenyl group spin and charge distributions in the anion radical and dianion, respectively. However, deuteriation of the phenyl moiety does not alter these distributions in the cyclooctatetraenyl moiety. The upfield shift in the chemical shifts of the phenyl carbons in the dianion and the increased spin density in the phenyl moiety in the anion radical, resulting from deuteriation of the eight-membered ring, is explained in terms of the different degrees of twist between the COT and phenyl rings. Since there is more zero-point energy in the coplanar arrangement and the force constant for C-D or C-H stretching mode should be maximized in a coplanar arrangement, [6]-[8]^*- will tend to be more twisted than will [6]-[8]-d₇^*-. The deuteriation studies have further shown that the nature of the spin distribution in the anion radical of [6]-[8] has long been fundamentally misunderstood.