Radical stabilization energies : The β-alkoxy group from kinetics of the thermal isomerization of 1-Chloro-4-methoxymethylbicyclo[2,2,0]hexane in the gas and liquid phase

Abstract

The kinetics of the thermal isomerization of 1-chloro-4-methoxymethyl- log(kb/s^-1) = (14.1 ± 0.2)-(36.2 ± 0.5)/θwhere θ = 2.303RT kcal/mol and the subscripts g, a, and b refer to the gas phase, nitrobenzene-d₅ as solvent, and diphenyl ether as solvent respectively. The Arrhenius parameters are discussed in terms of transition state estimates for a biradical mechanism. With reference to the isomerization of bicyclo[2,2,0]hexane and 1,4 dichlorobicyclo[2,2,O]hexane, the α-methoxymethyl group is shown to destabilize the biradical by 6.1 ± 2.4 kcal/mol by comparison with an α-propyl group. This radical destabilization by the β-ether oxygen atom is explained in terms of the inductive effect of the β-electronegative atom.