Predicting the entropy of boiling for organic compounds

This study aims to predict the entropy of boiling (Delta S-b) for organic c ompounds by considering parameters that are indicative of both molecular ge ometry and molecular association. The proposed method is a modification of Trouton's rule. It utilizes three geometric parameters, sigma, tau, and ome ga, that address molecular symmetry, flexibility, and planarity, respective ly, as well as a set of group contributors that focus on hydrogen-bonding a nd strong dipolar interactions. The molecular geometry parameters are uniqu e in that they reflect the ordering of molecules in the liquid that cannot be described by group contribution. The database of 903 organic compounds c overs a broad array of structural categories. The root mean square error fo r the prediction is 2.12 J/mol.K, which is very low given the diversity of the database. An independent entropy dataset of 31 compounds was used to sh ow that the proposed method is more accurate than four published methods. T he success of this approach illustrates the need for nonadditive structural parameters along with group additive parameters to characterize phase chan ge entropy.