Comment on "New statistical mechanical model for calculating Kirkwood factors in self-associating liquid systems and its application to alkanol+cyclohexane mixtures" [J. Chem. Phys. 127, 114501 (2007)].

A brief overview of the current state of the research on calculation of Kirkwood factor of liquid alcohols and their mixtures is presented. On the basis of the accurate solution for the correlation factor, obtained in the author's published papers, it was stated that the formulas for Kirkwood factor of alcohols g(K) and their mixtures with inert solvents (hydrocarbons) obtained in the paper by Vasiltsova and Heintz [J. Chem. Phys. 127, 114501 (2007)], in the opinion of the present author, are erroneous and contradict all preceding results obtained in this area of research. On the basis of the rigorous solution for Kirkwood factor of liquids with predominant chainlike aggregation it has been shown that the generally accepted opinion based on the famous Kirkwood formula g(K)=1+z, where z is coordination number, is average cosine of angle between adjacent dipoles in liquids ([J. G. Kirkwood, J. Chem. Phys. 7, 911 (1939)], Eq. (19)) that Kirkwood factor as determined by the mean cosine of the angle between adjacent dipoles should be modified for the liquids consisting of nonlinear molecules with the complex type of the supramolecular organization. Alcohols are examples of such liquids, in which long-range intermolecular correlations beyond the nearest coordination shells are essential for their structural organization.

Modeling of supramolecular structure and dielectric properties of butanols from melting point to supercritical state.

The supramolecular structure and dielectric properties of pure fluid butanols have been modeled in the temperature range from the melting point to the vicinity of the critical point using the quasichemical model of nonideal associated solution (QCNAS). The model of supramolecular structure takes into account both chain-like and cyclic aggregates. Dielectric permittivity and dipole correlation factor of n-, sec-, and tert-butanol are calculated in the temperature intervals 191-553, 166-533, and 298-503 K, respectively, using parameters obtained earlier for ambient conditions. The thermodynamic and structural parameters of supramolecular aggregation are reported. Size and structure distribution functions of aggregates are evaluated in the entire temperature range. Mean degree of aggregation of n-butanol decreases from hundreds at low temperatures to about 1.3 around critical point. The structure of n-butanol and s-butanol is characterized mainly by chain-like aggregation. tert-Butanol's degree of aggregation is about 4 at ambient conditions and falls to 1.4 approaching the critical point. The fractions of molecules in chain-like and cyclic aggregates are comparable for tert-butanol. This conclusion refutes the frequently expressed opinion that tert-butanol consists mostly of cyclic species.

Modeling of supramolecular ordering and physicochemical properties in cyclohexane-ethanol mixtures.

The quasichemical model of the nonideal associated solution (QCNAS) was used to analyze the excess thermodynamic functions and permittivity of cyclohexane-ethanol mixtures in the entire range of compositions and in a wide temperature range. A new model of supramolecular organization was substantiated, taking into account chain and cyclic aggregation of alcohol with the formation of chain aggregates of arbitrary size, which describes a set of physicochemical properties of this mixture with complicated behavior of both thermodynamic and dielectric properties. Equilibrium constants and thermodynamic parameters of H bonding having cooperative character and integral and differential characteristics of aggregation and the structural parameters of aggregates were determined. It was established that the role of nonpolar cyclic structures increases as alcohol concentration decreases. The model describes the permittivity of solutions in the entire range of compositions and reproduces a minimum of the dipolar correlation factor in the range of dilute alcohol solutions. The new data obtained on the supramolecular ordering characterized by the long-range molecular correlations due to H bonding are discussed in detail.