REACTIONS OF THE BENZYNE RADICAL-ANION IN THE GAS-PHASE, THE ACIDITY OF THE PHENYL RADICAL, AND THE HEAT OF FORMATION OF ORTHO-BENZYNE

The thermally equilibrated ion-molecule reactions of the o-benzyne radical anion have been examined in the gas phase with the flowing afterglow technique. By using the bracketing technique between o-C6H4.- and Bronsted acids of known acidity, we have established the gas-phase acidity of the phenyl radical as DELTA-G-degrees acid[C6H5.] = 371(-3)+6 kcal mol-1. Combination of our experimental acidity of the phenyl radical with appropriate thermochemical data from the literature yields a variety of substantially improved thermochemical values of C6H4 and C6H5. species, most notably, DELTA-H(f)-degrees [o-C6H4] = 105 kcal mol-1. In addition to behaving as a Bronsted base, o-benzyne radical anion is found to undergo a number of other reactions, including electron transfer, H/D exchange, H2+ transfer, and direct addition. The reaction between o-C6H4.- and the simple aliphatic alcohols is shown to be a competition between proton transfer and H2+ transfer while that between o-C6H4.- and dioxygen or 1,3-butadiene is found to be exclusively an associative detachment process. One unanticipated, novel observation from these studies is the facile formation of an addition complex between the o-benzyne radical anion and carbon dioxide, leading to a distonic radical anion (benzoate-type anion, phenyl-type radical) that offers a unique opportunity for examining radical chemistry in ion-molecule encounter complexes.