The radical stabilization energy due to an a-chlorine atom from the kinetics of the thermal isomerization of 1-Chlorobicyclo[2,2,0]hexane in the gas and liquid phase

Abstract

The rate of isomerization of 1-chlorobicyclo[2,2,0]hexane to 2- chlorohexa-1,5-diene, both in the gas phage and in solution, has been measured over the temperature range 409-497 K. The Arrhenius parameters derived from these rates are represented by the equations                               log(kg/s^-1)=(13.49±0.08)-(148.2±0.6/θ                               log(ka/s^-1)=(13.21±0.12)-(144.44±0.50)/θ  and                              log(kb/s-1)=(13.25±0.44)-(144.8±1.6)/θ where the subscripts g, a and b refer to the gas phase, tetrachloroethylene as solvent and o-dichloro-benzene as solvent respectively, θ = 19.15 kJ mol^-1 and the errors are least-squares deviations. A radical stabilization energy of 5±2 kJ mol^-1 for the α- chlorine atom derived from these Arrhenius parameters is in excellent agreement with the value derived from kinetics of the isomerization of 1,4-dichlorobicyclo[2,2,0]hexane and from the thermochemistry of chloroethyl radicals.