Vibrational spectroscopic studies on the state of aggregation of water in carbon tetrachloride, in dioxane and in the mixed solvents

Abstract

A detailed infrared study of the vibrational modes of water in dioxane, carbon tetrachloride and a mixed solvent as a function of concentration is reported. H 2O/D 2O mixtures have been used in order to isolate the uncoupled v(OH) and v(OD) modes. The data have been interpreted in terms of the state of aggregation of water molecules in a hydrophobic solvent and in a solvent to which hydrogen bonding can occur. It is shown that at very low concentrations ( x H 2O = 5×10 −4) water exists in the monomeric form and can rotate rather freely. However, water is strongly self aggregated in a hydrophobic organic solvent for concentrations greater than x H 2O = 5×10 −3 (ie if there are more than 5 water molecules in a 1000 solvent molecule ‘bath’). Evidence of distinct (dioxane) m(water) n complexes is found in dioxane solution and in the mixed solvent. However, as the water concentration is increased it is clear that a water/solvent ‘network’ is formed. The aggregation processes involving water depend critically, however, on the hydrophobicity of the solvent mixture.