Gas phase ion chemistry of the vinylidene radical anion and the acidity of the vinyl radical

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Quantitative and qualitative aspects of the thermally equilibrated (298±3 K) reactions of vinylidene radical anion with a variety of neutrals have been examined in the helium filled (0.20–0.40 Torr) reactor of a flowing afterglow. The bracketed acidity of the vinyl radical, Δ H° acid(H 2CC H ) = 385± 3 kcal mol −1, is the first experimental measurement of this important quantity. From this experimental acidity of the vinyl radical and appropriate information from the literature, we derive an estimate of the heat of formation of the vinyl radical, Δ H° f(H 2CCH − ) = 67.9± kcal mol −1, the CH bond dissociation energy in ethylene as BDE(HCHCH 2) = 107.6± kcal mol −1 and a CH bond dissociation energy in the vinyl radical as BDE(HCCH 2) = 82.7± kcal mol −1. H 2CC − is found to display a number of efficient reaction channels with various neutral reagents including proton transfer, electron transfer, atom transfer and associative detachment. For those reactions involving an electron transfer component, a reaction scheme involving first electron transfer, then vinylidene-to-acetylene isomerization and finally proton transfer, is proposed as a convenient tool with predictive capability.