Predicting the Entropy of Boiling for Organic Compounds

This study aims to predict the entropy of boiling (ΔS_b) for organic compounds by considering parameters that are indicative of both molecular geometry and molecular association. The proposed method is a modification of Trouton's rule. It utilizes three geometric parameters, σ, τ, and ω, that address molecular symmetry, flexibility, and planarity, respectively, as well as a set of group contributors that focus on hydrogen-bonding and strong dipolar interactions. The molecular geometry parameters are unique in that they reflect the ordering of molecules in the liquid that cannot be described by group contribution. The database of 903 organic compounds covers a broad array of structural categories. The root mean square error for 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 show that the proposed method is more accurate than four published methods. The success of this approach illustrates the need for nonadditive structural parameters along with group additive parameters to characterize phase change entropy.