Dielectric study of the rotational equilibria of succinonitrile

Abstract

Dipole moment techniques and the non-linear dielectric effect have been applied to the study of environmental influences on the conformational equilibrium in dilute solutions of succinonitrile (1,2-dicyanoethane). The trans–gauche equilibrium constant K and the dipole moment of the gauche conformer were simultaneously and unequivocally determined in the temperature range from 288 to 318 K. The enthalpy and entropy of the reaction were determined as a function of the dielectric permittivity of the solvent and indicated enhanced stability of the gauche form in polar environments. The effect is interpreted in terms of electrostatic solvation energy. The role of the orientation of the solvent molecules in the field created by the dipolar conformer outside the cavity is emphasized.