High-pressure and density dependence of H-bond complexes in solutions. A spectroscopic study of intermolecular interactions

Abstract

In ternary systems of H-bonded complexes of perfluoro- tert.-butanol (PFTB) with propionitrile, acetone, dioxane or tetrahydrofuran dissolved in polychlorotrifluoroethene (PCFE), increase of pressure induces (1) an increase of the OH frequency shift 1 1 Δν = (gas phase) − ν(p). up to a maximum, Δν max, (2) a decrease of Δν at pressures higher than 2–3 GPa. This is contrary to the pressure behaviour of PFTB complexes with aromatic acceptors, which reveal an increase of the shift in the whole investigated pressure range up to 8 GPa. The pressure—density relation of the solvent PCFE has been determined. At 5 GPa the volume is reduced to 69% of the volume under ambient conditions. The pressure-induced maximum shift in the case of the medium strong H-bonds is probably due to the distortion of the optimal H-bond configuration. This conclusion is confirmed by results for alcohol self-associates, for which the number of H-bonds increases up to pressures of about 3 GPa and then decreases at higher pressures. A qualitative interpretation of the high-pressure results is given from the viewpoint of a linear model.