Estimation of Total Entropy of Melting of Organic Compounds

The aim of this study is to provide a simple means of estimating the total entropy of melting (Δ ) for a wide range of pharmaceutically and environmentally relevant organic compounds. A semiempirical equation based on only 2 molecular descriptors, the rotational symmetry number(σ) and the molecular flexibility number (Φ), has been used to calculate Δ for 1799 organic compounds. The average absolute error in estimating Δ is 12.3 J/K·mol. This method gives entropy predictions that are comparable to those of a recently published group additivity method that utilizes 144 group contribution values.