Thermal isomerization of cyclobutenes. Part 13.—1-n-Propylcyclobutene, 1-isopropylcyclobutene, 1-allylcyclobutene and 1-cyclopropylcyclobutene

Abstract

The thermal isomerizations of 1-n-propyl, 1-isopropyl, 1-allyl and 1-cyclopropyl cyclobutenes have been studied in the gas phase at temperatures in the range 145–200°C. The isomerizations are almost certainly unimolecular and were investigated in their high pressure region. Rate constants for the reactions yielded the Arrhenius equations: 1-n-propyl, k= 10^13.55 exp (–34,546/RT) sec^–1; 1-isopropyl, k= 10^13.55 exp (–34,669/RT) sec^–1; 1-allyl, k= 10^13.48 exp (–34,200/RT) sec^–1; 1-cyclopropyl, k= 10^13.48 exp (–34,140/RT) sec^–1. The effect of alkyl substitution on the free energy of activation for the isomerization of the cyclobutenes is discussed.