Conformational analysis of model compounds of non-ionic surfactants in aqueous solution: Raman spectroscopy and ab initio MO calculations

Abstract

The conformation of 1,2-dimethoxyethane and 2-methoxyethanol in aqueous solution has been studied by Raman spectroscopy and ab initio molecular orbital (MO) calculations. The Raman spectra have been interpreted by normal coordinate analysis with the force constants evaluated by the MO calculations. The conformational analysis of the two compounds has shown that both the (C)OCH 2-CH 2O(C) and (C)OCH 2−CH 2OH groups preferentially adopt the gauche conformation in water. This conformational behavior contrasts with that in the neat liquid, where the trans conformation is much more favored than in aqueous solution. The gauche preference of the OCH 2−CH 2O group in water is associated with the formation of a stable water structure with oxyethylene (OE) chains favorably incorporated. This cooperative effect of the OE chain conformation and the water structure is one of the most specific features of the OE chain—water system.