Proton transfer reactions of C₂H₄^{{radical dot}+}: the bond energy D(C₂H₃-H)

Reactions of C₂H₄^{{radical dot}+} with a series of molecules having different proton affinities were studied with a selected-ion flow tube in order to bracket the proton affinity (PA) of the C₂H₃^{{radical dot}} radical. Since the proton transfer reactions were studied only in the forward direction, the PA values were obtained from correlations between the efficiency of proton transfer and the overall reaction thermochemistry. Reactions with CH₃OH and CClH₂CN were particularly relevant and yielded PA(C₂H^{{radical dot}}₃) = 182.2 ± 1 kcal mol^-1 at 298K. A thermochemical cycle leads to the bond energy D₂₉₈(CH₂CHH) = 110.9 ± 1 kcal mol^-1, in excellent agreement with recent data based on negative ion acidity experiments.