Dipole-dipole interactions and their role in relaxation processes in polar solvents

Abstract

Data for Δ H τ, the enthalpy of activation determining the temperature dependence of the Debye relaxation time have been collected and compared for polar aprotic solvents of lower molecular weight. It is shown that the variation in this quantity with solvent can be largely attributed to a corresponding variation in dipole-dipole interaction energy when the latter quantity is estimated by a model in which the solvent is represented as hard sphere with a centrally embedded point dipole. It is also shown that the appropriate quantity to be considered for alcohols in such a comparison is the value of Δ H τ for the second relaxation process, that is, rotational diffusion. The Δ H τ data are also used to consider the variation in enthalpy of activation for electron transfer reactions with solvent, and the role of solvent dynamical processes in determining the rate constants for these reactions.