SCHEDULED MAINTENANCE
The kinetics and mechanism of ring opening of radicals containing the cyclobutylcarbinyl system
Abstract
The kinetic parameters for β-fission of radicals containing the cyclobutylcarbinyl system have been determined by analysis of the mixtures obtained when suitable chloro-compounds are treated with tributylstannane. Under these conditions ring opening is irreversible and in the rigid bicyclic system (4) is under stereoelectronic control. For ring opening of cyclobutylcarbinyl radical (8)kf= 4.3 × 103 s–1 at 60°, and the best values of the activation parameters appear to be ΔH‡= 12.2 kcal mol–1 and ΔS‡=–7.4 cal mol–1 K1. Monocyclic systems undergo preferential fission of the more substituted βγ-bond. Methyl substituents at the α-, β-, or δ-positions have little effect but γ-substitution strongly enhances the rate of ring opening. The transition state is reactant-like and has a similar disposition of centres to that (1) for homolytic addition.
Please wait while we load your content...
