The dipole moment of alcohols in the liquid phase and in solution

Abstract

Understanding polarization effects in condensed phases, like liquids and solutions, requires computational methods that can accurately predict dipole moments and energy of polarized molecules. In this paper, we report an improvement and extension of our recently developed Self-Consistent Electrostatic Embedding (SCEE) method, and apply it to determine the dipole moment of pure liquid alcohols, as well as of methanol dissolved in a variety of solvents (namely, other alcohols, water and hexadecane). We observe that the dipole moments of pure liquid alcohols are enhanced by ∼0.9 D over their gas phase values, which is similar to the dipole enhancement previously observed for water, and much higher than what is predicted by dielectric continuum models. Our results demonstrate the importance of accounting for local solvation effects, namely the formation of hydrogen bonds, when calculating the extent of liquid phase polarization. In fact, we argue that the dipole enhancement upon solvation can be explained as a superposition of two effects: bulk screening described by the solvent dielectric constant and local solvation that requires a discrete molecular-level description of the system. SCEE is able to account for both effects simultaneously, and is thus a powerful tool to estimate polarization effects in liquids and solutions.