Solvation spectra. Part 44.—Nuclear magnetic resonance study of binary solvent mixtures: water structural effects

Abstract

The hydroxyl proton resonance frequency for various binary solvent mixtures, including water with methanol, t-butyl alcohol, triethylamine and acetone, has been measured over the complete mole fraction range. Results of similar experiments for alcohol + alcohol and alcohol + amine mixtures are used for comparative purposes. At low concentrations water behaves normally in these solvents, but in the water-rich region shifts to low-field were generally observed, especially for aqueous alcohols and amines. These are interpreted in terms of an acid-base effect, and an effect involving local changes in water structure, equivalent to a temperature reduction. Various methods for differentiating between these two factors are outlined. It is concluded that for aqueous methanol, the acid-base effect dominates, whilst for aqueous t-butyl alcohol the water-structure effect is of major significance. Other solvents fit between these extremes.