Isomerization of Allene Propyne in Shock Waves and ab Initio Calculations

Article abstract of DOI:10.1021/j100285a040

The isomerization allene <=> propyne has been studied behind shock waves over the temperature range between 1300 and 2100 K and the total density range of (0.6-2.4) x 1E-5 mol/cm³.The isomerization rate was monitoring by means of the IR emission from allene and propyne.It was found that the process proceeded in the fall-off region, and the high-pressure limit rate constants were determined as k₁ = 1E14.34 exp<-68.1 kcal mol^-1/(RT)> s^-1, for the isomerization of allene to propyne, and k_-1 = 1E14.14 exp<-69.7 kcal mol^-1/(RT)> s^-1, for the isomerization of propyne to allene, using the equilibrium constants.Ab initio molecular orbital calculations have also been performed for the isomerization.It was found that the isomerization proceeded in a series of successive reactions via cyclopropene, which has been suggested by Honjou et al. (Honjou, N.; Pacansky, J.; Yoshimine, M.J.Am.Chem.Soc. 1984, 106, 5361).The rate constants estimated in terms of the transition-state theory, k₁ = 1E14.23 exp<-66.6 kcal mol^-1/(RT)> s^-1 and k_-1 = 1E14.12 exp<-67.0 kcal mol^-1/(RT)> s^-1, are consistent with the experimental results.<