STRUCTURE OF COMPLEXES IN HCl–ISOPROPYL ALCOHOL SOLUTIONS AND EQUILIBRIUM COMPOSITION OF THE SYSTEM

Structure, energy and spectral parameters of moieties of C 3 H 7 OH–HCl solutions with various compositions are calculated using density functional theory based on the regularities characterizing formation of complexes with hydrogen bonds in binary systems. It is shown that six concentration structural zones can be distinguished in the C 3 H 7 OH–HCl system (1:0-6:5). Liquid isopropyl alcohol consists of cyclic hexamers (C 3 H 7 OH) 6 . Solutions of each of the five subsequent zones contain two types of cyclic moieties whose average H-bond energies (~30-74 kcal/mol) are 5-10 times larger than those in hexamer (C 3 H 7 OH) 6 . The main interactions between components in the C 3 H 7 OH–HCl system occur inside such moieties (almost completely isolated from each other by alkyl groups of C 3 H 7 OH molecules). Such moieties contain previously unknown complexes with two quasi-symmetric bridges Cl⋯H⋯O and O⋯H⋯O, conjugated proton solvates, having one common oxygen atom. The concentrated solutions contain, in addition to conjugated proton solvates, moieties with the composition 2:2, each having four Cl⋯H⋯O bridges with similar parameters. The fact that the maximum density of these solutions and the HCl solubility limit approximately correspond to the component mole ratio 6:5 was explained and all features of obtained IR spectra were interpreted by using calculated data on the structure of C 3 H 7 OH–HCl solutions and that of observed complexes.