PROTON-TRANSFER REACTIONS OF (C2H2)-H-(+.) - THE BOND-ENERGY D0(C2H-H)

Reactions of C2H+{radical dot}2 with a series of molecules having different proton affinities were studied on a selected ion flow tube (SIFT) in order to bracket the proton affinity of the C2H{radical dot} radical. Reactions with XCN (X = Cl, Br) were particularly relevant and yielded PA (C2H{radical dot}) = 175 ± 1 kcal mol-1 at 298 K. A thermochemical cycle leads to the bond energy D0 (C2HH) = 123 ± 1 kcal mol-1. Since the proton transfer reactions were studied only in the forward direction, these values were obtained from correlations between the efficiency of proton transfer and the overall reaction thermochemistry. The observation of H{radical dot} atom transfer from C2H2 to NH+{radical dot}3 verifies the rather low bond energy in acetylene. © 1990.