Entropy convergence in the hydration thermodynamics of n-alcohols.

Using experimental data from the literature, entropy convergence in the hydration thermodynamics of n-alcohols is shown to occur at about 125 degrees C. The phenomenon is reproduced in a more-than-qualitative manner by means of a theoretical approach that accounts for the entropy contributions associated with (a) creation of a cavity in water, (b) turning on solute-water van der Waals interactions, and (c) turning on the solute-water H-bonding potential. The density of water and the effective size of water molecules with their temperature dependence play the pivotal role for the occurrence of entropy convergence, together with the property of the alcohol hydroxyl group to form the same number of H-bonds with water molecules regardless of the length of the alkyl chain.