Studies of Hydrophobic Bonding in Aqueous Alcohols: Enthalpy Measurements and Model Calculations

The coefficients which measure the contribution of a pair of solute molecules to the excess enthalpy have been measured in water at 25 degrees C for all pairs of alcohols which can be formed from the series methyl to n-butyl plus t-butyl as well as for ethanol with some of the higher alcohols and with the n-alkyl sulfonates through octyl. The methylene-group contribution to these coefficients is readily identifiable in suitable cases. These data and the corresponding free-energy and volume coefficients, where they are known, are analyzed in terms of a model which specifies the core repulsion and solvation-layer overlap terms in the potential for the interaction of two solute molecules. The latter term has an adjustable parameter, the so-called Gurney free-energy parameter which is adjusted for each solute pair to fit the free-energy data. Its temperature and pressure derivatives are adjusted to fit the enthalpy and volume data, respectively. These parameters are compared with the corresponding thermodynamic coefficients of solvation as far as possible.