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 molecu lar 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, where as the latter is calculated using a modification of Walden's rule. Approxim ately 1040 melting point data were compiled and analyzed by multiple regres sion. The root-mean-square error of the estimation is 34.4 K. This is relat ively 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 Re id(8) was performed on 50 aliphatic compounds that were not used in the tra ining set. The average absolute error for this method is approximately 20%, whereas that for the Joback and Reid data is 34%. The higher prediction ac curacy of the proposed method suggests that the melting point prediction ca n better be approached by using both group contribution (enthalpic) and sim ple molecular geometric parameters (entropic).