Thermal unimolecular isomerisation of cis-hexa-1,3-diene

Abstract

cis-Hexa-1,3-diene isomerises in the gas phase by a first-order homogeneous process to yield cis,trans-hexa-2,4-diene as the major product. Small amounts of cis,cis-hexa-2,4-diene are also formed, partly direct from the reactant and partly as a secondary product from the initially formed cis,trans-diene. In the temperature range 475–518°K the rate constants for the isomerisation to the cis,trans-hexa-2,4-diene fit the Arrhenius equation k= 10^10·80 exp(–32,500/RT) sec.^–1.

The rate constants are independent of pressure in the range 2–70 mm. The reaction is considered to be truly unimolecular, proceeding through a 6-centre, hydrogen-bridged transition state.