A combined group contribution and molecular geometry approach for predicting melting points of aliphatic compounds

A combined approach that utilizes both group contribution and simple molecular geometric parameters is employed to predict normal melting points for a variety of aliphatic compounds. The melting points are estimated from the ratio of the enthalpy and the entropy of melting. The former is calculated from the sum of enthalpic group contributions and correction factors, whereas the latter is calculated using a modification of Walden's rule. Approximately 1040 melting point data were compiled and analyzed by multiple regression. The root-mean-square error of the estimation is 34.4 K. This is relatively low given the complexity of melting and the diversity of the database used. A comparison of the proposed method with the method of Joback and Reid was performed on 50 aliphatic compounds that were not used in the training set. The average absolute error for this method is approximately 20%, whereas that for the Joback and Reid data is 34%. The higher prediction accuracy of the proposed method suggests that the melting point prediction can better be approached by using both group contribution (enthalpic) and simple molecular geometric parameters (entropic).