The thermal unimolecular isomerisations of 1,1-dicyclopropylethylene and 1-cyclopropylcyclopentene

Abstract

These thermal isomerisations have been studied in the gas phase in the temperature range 342–389·5°. 1,1-Dicyclopropylethylene isomerises by a first-order homogeneous reaction, to yield 1-cyclopropylcyclopentene. In the same temperature range the cyclopropylcyclopentene itself undergoes a homogeneous first-order reaction to yield bicyclo[3,3,0]oct-1-ene. The rate constants for both isomerisations are independent of pressure in the range 1–5 mm. and also in the presence of added nitrogen (200 mm.). Both isomerisations are almost certainly true unimolecular reactions. The rate constants fit the Arrhenius equations: k(dicyclopropylethylene)= 10^14·29 exp(–51,060/RT) sec.^–1, k(cyclopropylcyclopentene)= 10^14·01 exp(–51,290/RT) sec.^–1.

This appears to be the first study involving two consecutive unimolecular processes that has been followed in detail in the same system.