The Fusion of Di-Substituted Benzines
The entropy of fusion of a homologus series of di-substituted benzene compounds was shown by multiple linear regression to be approximately constant, with a mean value of 12.7 e.u. and a standard deviation of less than 2.0 e.u. The series of compounds were selected to emphasize molecular interactions, and to minimize differences in geometry. These results disagreed with Bondi1s prediction. He suggested that strong molecular dipoles and hydrogen bonding would restrict free rotation of the molecules in the liquid, decreasing the gains in orientational freedom on melting, which would result in a decrease in the entropy of fusion. The fact that these results Were not observed was attributed to corresponding restrictions of the torsional vibrations in the crystals. This is believed to compensate for the association in the liquid, so that the ratios of molecular freedom between the crystal and the melt remain the same.