Hindered Internal Rotation and Dielectric Relaxation

Abstract

A model calculation of the dielectric behavior of a liquid whose molecules have conformation‐dependent dipole moment components is presented. The molecules contain two groups of equal size which interact according to parabolic and cosine potentials of varying symmetry. The calculated dielectric behavior is discussed in terms of the model parameters. Measurements of dielectric permittivities and losses of 4‐bromobiphenyl in dilute solution with carbon tetrachloride at 20, 30, and 40°C are interpreted in light of the model calculation. Measurements of dielectric permittivities and losses of 2,2′‐bipyridine and 2,2′‐dibromobiphenyl in dilute solution with carbon tetrachloride at 10–40°C are interpreted in light of a model calculation involving hindered internal rotation reported previously. The advantages and limitations of the dielectric method for characterizing hindered internal rotation in molecules in the liquid state are discussed.