Compensation relationship in thermodynamics of solvation and vaporization: Features and applications. II. Hydrogen-bonded systems

Abstract

There is a well-known extrathermodynamic correlation between the entropies (or Gibbs energies) and enthalpies of many processes, including solvation and vaporization, called the compensation relationship. Non-hydrogen-bonded species, from rare gases to organic non-electrolytes, follow a common correlation between the Gibbs energies and enthalpies of solvation in solvents incapable of self-association. The Gibbs energies of solvation of apolar molecules in hydrogen-bonded solvents and ionic liquids tend to deviate towards the higher values on the compensation plot, which is known to be a manifestation of the solvophobic effect.However, there are more options for hydrogen bonding upon solvation, whose effect on the compensation relationship has not yet been studied, either qualitatively or quantitatively. In this work we classified hydrogen-bonded solute–solvent systems into the three types and quantitatively investigated the deviations arising in each case: 1) apolar solutes solvated in hydrogen-bonded solvents (e.g., octane in water); 2) solutes capable of hydrogen bonding with non-self-associated solvents (chloroform in pyridine); 3) solutes capable of hydrogen bonding with hydrogen-bonded solvents (chloroform in ethanol).Furthermore, we have shown how to predict the solvation enthalpies in various hydrogen-bonded systems, knowing the Gibbs energies of solvation and the molecular structures of the solute and solvent. The agreement between the predicted and literature values (RMS < 1.5 kJ·mol−1, N = 211) confirmed the regularities observed in each case.