Molecular symmetry, melting temperatures and melting enthalpies of substituted benzenes and naphthalenes

Thermodynamic parameters of melting for mono- and di-substituted benzenes and naphthalenes have been examined. Correlations with molecular structural parameters are discussed. With very few exceptions, ortho- and meta-disubstituted benzenes melt at lower temperatures than para-isomers, an enthalpic effect related to crystal cohesion. However, no significant correlation was found between melting temperature and crystal density or packing energy. The concept of molecular shape and symmetry is discussed in connection with the stability of crystal packing.