Supramolecular organization and physicochemical properties of cyclohexane-ethanol solutions and the role played by cyclic aggregates of the alcohol

Based on the quasi-chemical model of nonideal associated solutions (QCNAS), we analyzed the excess thermodynamic functions (Gibbs free energy, enthalpy, and entropy) and the dielectric permittivity of cyclohexane-ethanol solutions over the entire range of concentrations and a wide temperature interval. It was demonstrated that a model of the supramolecular organization taking into account the chain and cyclic association of the alcohol via O-H...H hydrogen bonds describes a number of physicochemical properties of solutions. The corresponding equilibrium constants, enthalpies and entropies of association, and the structural parameters of supramolecular aggregates were determined. Various integral and differential characteristics of supramolecular aggregation; including the degrees of association and the functions of distribution of molecules over chain and cyclic associates and over numbers of H-bonds formed, were calculated. The effect of low-polarity cyclic structures was shown to increase with decreasing alcohol concentration. The excess Gibbs free energy and enthalpy of the solution are largely determined by the positive contributions from O-H...H hydrogen bonds. The proposed model describes the dielectric permittivity of the solution over the entire range of compositions and reproduces the experimentally observed minimum in the dipole correlation factor for diluted alcohol solutions. A relatively small fraction of cyclic alcohol associates produces a significant effect on the properties of the solution. Models taking into account only a limited number of associates (one or two) were demonstrated to be incorrect.