The thermal isomerization of 1,1-dimethyl-2-vinylcyclopropane to cis-2-methylhexa-1,4-diene via 1,5-hydrogen migration

The gas phase isomerization of 1,1-dimethyl-2-vinylcyclopropane to cis-2-methylhexa-1,4-diene has been studied in a static system. The isomerization is homogeneous and kinetically first order. The rate constants were independent of initial reactant pressure in the range 0.6 to 2 torr and of added nitrogen up to 180 torr. Rate constants determined at 10 temperatures in the range 200 to 254°C fitted the Arrhenius equation k = 10^11.41±0.02 exp (?33,540 ± 47 cal/RT) sec^?1 The low A factor and activation energy are consistent with a concerted 1,5-hydrogen migration via a “tight” cyclic transition complex.