On the dielectric continuum solvent model for theoretical estimates of the conformational equilibrium of molecules with an intramolecular hydrogen bond Original Research Article

Theoretical calculations of solvation energies for molecules with an intramolecular hydrogen bond have been performed using two types of continuum dielectric solvation models. One is the Onsager–Kirkwood–Abraham model (OKA) with a simple spherical cavity and the other is a polarized continuum (overlapping spheres) model (PCM) with a bubble-shaped solvent accessible surface. The solvation energies by the PCM model are several times larger than those by the OKA model. Nevertheless, the both models provide approximately consistent results with each other for differences in solvation energy, ΔEsolv, between intramolecularly hydrogen bonded conformers and hydrogen-bond-free conformers. These results roughly reproduce the experimental values which were previously obtained by variable-temperature infrared spectroscopy. However, the agreement between the calculations and the experimental results is not satisfactory and not improved even by using the PCM model with the sophisticated solvent accessible surface instead of the simple OKA model. The problem might be attributed to a defect of the dielectric continuum approximation of solvent.