Interpretation of experimental hydrogen-bond enthalpies and entropies from COSMO polarisation charge densities

Abstract

In this work, experimental hydrogen-bond (HB) enthalpies measured in previous works for a wide range of acceptor molecules in dilute mixtures of 4-fluorophenol in non-polar solvents are quantified from COSMO polarisation charge densities σ of HB acceptors (HBA). As well as previously demonstrated for quantum chemically calculated HB enthalpies, a good correlation of the experimental data with the polarisation charge densities is observed, covering an extended range of HBA (O, N, S, π systems and halogens) ranging from very weak to strong hydrogen bonds. Furthermore, for the first time, a quantitative analysis of experimental HB entropies is performed for such a chemical diversity of HBA. A good quantification of these entropies is achieved using the polarisation charge density σ as a descriptor in combination with the logarithm of a directional partition function Ω_HB. This partition function covers the directional and multiplicity entropy of HBA and is based on the σ-proportional HB enthalpy expression taken from COSMO-RS. As a result, the experimental HB enthalpies and free energies of the ∼300 HB complexes are quantified with an accuracy of ∼2 kJ mol⁻¹ based on COSMO polarisation charge densities.