Medium effects on rotational equilibria. Part III. The theory for any number of dipoles and its application to 1,1,2-trichloroethane

Abstract

An electrostatic theory of the effect of the medium on the energy differences between rotational isomers, previously given only for very simple molecules, is generalised to apply to any solute molecule. The theory is applied to 1,1,2-trichloroethane and shown to give good agreement with the experimental values of the energy difference between the rotational isomers in the liquid and vapour states. The proton coupling constants of the rotational isomers can be obtained by use of the theory from the solvent-dependence of the observed coupling constant and are 2·2 and 6·38 c./sec., respectively, for the gauche and trans isomers. Certain exceptional solvents are considered as either preferentially associating with one isomer or preferentially solvating the solute with polar groups in the solvent.