Infrared and nuclear magnetic resonance studies pertaining to the cage model for solutions of acetone in water

Abstract

Solutions of acetone in water show a single CO stretching mode in the infrared (1697 cm^–1), which is assigned to acetone hydrogen bonded to two water molecules. On cooling below 0 °C new features appear which are characteristic of concentrated solutions of acetone, formed by growth of ice crystals. These bands are assigned to acetone forming single hydrogen bonds (1708 cm^–1) and no hydrogen bonds (1715 cm^–1). The latter band is characteristic of bulk acetone. On standing at ca.–30 °C, all these features decay, and ultimately only a single narrow band is detectable at 1722 cm^–1, which is characteristic of isolated acetone molecules in completely inert solvents. This change is clearly a result of clathrate formation.

These results demonstrate unequivocally that acetone in liquid water is solvated in a manner that differs completely from cage “solvtion”. This remarkable difference between solid and fluid systems is interpreted in terms of the presence of large concentrations of free OH groups in liquid water.