Thermal unimolecular reactions of vinylcyclobutane and isopropenylcyclobutane

Abstract

The thermal decomposition of vinylcyclobutane proceeds by two pathways both of which are homogeneous first order processes. One reaction channel (k₁) yields butadiene and ethylene, the other (k₂) cyclohexene. Arrhenius equations have been obtained for both pathways from rate constants determined in the temperature range 296 to 366°C, viz: log k₁/s^–1= 14.87 ± 0.07 –(212,200 ± 800) J mol^–1/RTln 10, log k₂/s^–1= 13.86 ± 0.13 –(203,500 ± 1500) J mol^–1/RT ln 10. The thermal decomposition of isopropenylcyclobutane has been reinvestigated and found to be analogous to the vinyl compound. Arrhenius parameters have been obtained for its two modes of decomposition. All the reactions appear to be true unimolecular transformations. The potential energy surfaces for these decompositions and the back reactions are discussed.