Reactions of the Benzyne Radical Anion in the Gas Phase, the Acidity of the Phenyl Radical, and the Heat of Formation of o-Benzyne

Article abstract of DOI:10.1021/ja00016a001

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 Broensted acids of known acidity, we have established the gas-phase acidity of the phenyl radical as ΔG deg_acid.> = 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, ΔH_fdeg = 105 kcal mol^-1.In addition to behaving as a Broensted 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.