Investigations of structure and conformation. Part 8. E.s.r. Studies of conformational preferences, radical-centre inversion, and restricted rotation about ·C–CH3 in some 1,3-dioxolan-2-yl radicals

Abstract

The e.s.r. spectrum of 2-methyl-1.3-dioxolan-2-yl shows two temperature-depender line width phenomena. As the temperature is lowered the central lines of the quartet from the methyl-group pro ns become broader than the outside lines and the quintet from the γ-protons shows line width alternation. These effects are interpreted in terms of restricted rotation about ·C–CH₃(indicative of a bent radical centre) and radical centre inversion, respectively. Conformational analysis of the low-temperature splittings for this and sorre ring-substituted radicals has been carried out with the aid of INDO calculations: it is concluded that preferred conformations, which are to a certain extent dependent on the ring substituents, are of a type intermediate between envelcre and twist-chair forms (with a low barrier to pseudo rotation).