Relationship between the vaporization enthalpies of aromatic compounds and the difference between liquid and ideal gas heat capacities

Abstract

Understanding connection between physicochemical parameters, molecular structure and heat capacity of liquids remains limited, especially for complex organic molecules. One of possible ways to resolve this problem is analysis of difference between the liquid and ideal gas heat capacities. This difference also defines the temperature dependence of vaporization enthalpy. This work is based on the assumption that the difference between the liquid and gas phase heat capacity is primarily related to intermolecular interactions in the liquid. As the measure of intermolecular interactions, the vaporization enthalpy at 298.15 K was considered. The relationship between the difference of liquid and gas phase heat capacities and the vaporization enthalpy was analyzed for a wide range of aromatic and heteroaromatic compounds. An excellent correlation was observed (residual standard deviation 3.7 J·K−1·mol−1, N = 99). This correlation appeared to be useful for estimation of the vaporization enthalpies of aromatic compounds at elevated temperatures solely from the value at 298.15 K. The calculated and literature vaporization enthalpies measured between 360 and 650 K of 80 compounds from 134 sources were compared. An average absolute deviation of 1.5 kJ·mol−1 was observed, being competitive with the experimental errors of vaporization enthalpy determination.