Structural Order in the Hydration Shell of Nonpolar Groups versus that in Bulk Water

The poor solubility of nonpolar compounds in water around room temperature is governed by a large and negative entropy change, whose molecular cause is still debated. Since the Frank and Evans original proposal in 1945, the large and negative entropy change is usually attributed to the formation of ordered structures in the hydration shell of nonpolar groups. However, the existence of such ordered structures has never been proven. The present study is aimed at providing available structural results and thermodynamic arguments disproving the existence of ordered structures in the hydration shell of nonpolar groups. Poor solubility of nonpolar compounds in water at room temperature is governed by a large negative entropy change. The latter is usually attributed to the formation of ordered structures in the hydration shell of nonpolar groups; the existence of such ordered structures has never been proven. I provide available structural data and thermodynamic arguments disproving the existence of ordered structures in the hydration shell of nonpolar groups. image