Reaction of singlet methylene with methylenecyclopropane. Part 2.—High energy reaction pathways for chemically activated insertion products

Abstract

The reaction of singlet methylene, formed by the photolysis of keten (λ≃ 313 nm) with methylenecyclopropane has been investigated over the pressure range, 1–300 Torr, but predominantly at the lower end. The products are ethylene, propylene, acetylene, allene, spiropentane, methylenecyclobutane, methylmethylenecyclopropane (MMCP), ethylidenecyclopropane (ECP), isoprene and various penta-1,2-, penta-1,3- and penta-1,4-dienes. Studies of the pressure dependences of acetylene, isoprene and the pentadienes indicate that they originate from the chemically activated insertion products MMCP and ECP. Detailed consideration of the pressure dependences of the acetylene and isoprene yields in conjunction with RRKM calculations, provides support for multistep collisional deactivation in this system. A stepladder model with a deactivation step size of ≃ 7.2 kcal mol–1 fits the data.Further RRKM calculations are used together with this model to provide approximate values for the critical energies of the pentadiene forming pathways.