Directive effects in benzylic hydrogen atom abstraction. Part III. Chlorination of nuclear-substituted toluenes, diphenylmethanes, and ethylbenzenes

Abstract

The relative reactivities of nuclear-substituted toluenes, diphenylmethanes, and ethylbenzenes towards the benzene–chlorine atom π complex at 40° have been determined using sulphuryl chloride and t-butyl hypochlorite in benzene as reagents. The results show ρ values of –0·83, –0·65, and –0·67 for the former reagent and –0·81, –0·66, and –0·65 for the latter, all well correlated by the Hammett equation. Similar deuterium isotope effects k_H/k_D of 2·4 for [α,α-²H₂]toluene, and of 1·8 for [α,α-²H₂]diphenylmethane for the two reagents also provide strong evidence that the benzene–chlorine atom π complex is the principal hydrogen-abstracting species for benzylic chlorination with these reagents in benzene solution.