New aspects in the thermochemistry of solid-liquid phase transitions of organic non-electrolytes

The present paper is devoted to relationship between the fusion enthalpies of aromatic compounds at the melting temperature and the solution enthalpies in benzene at 298.15 K. Sublimation and vaporization thermochemistry are used as an additional source of information about the latter relationship. Depending on the magnitude of deviation between the solution enthalpies in benzene at 298.15 K and fusion enthalpies at the melting temperature, aromatic compounds are conventionally divided into three groups. For a large number of aromatic compounds not capable of self-association the equality between the fusion enthalpies at the melting temperature and the solution enthalpies in benzene at 298.15 K is established. For self-associated aromatic compounds the solution enthalpy in benzene at 298.15 K exceeds the fusion enthalpy at the melting temperature, and insertion of a substituent not forming inter- and intramolecular hydrogen bonds does not affect the difference between the solution and fusion enthalpies. The enthalpies of solution in benzene at 298.15 K of several aromatic compounds not capable of self-association appear to be visibly less than the fusion enthalpies at the melting temperature. The reasons of different relationships between the fusion and solution enthalpies are analyzed using Kirchhoff's law for the fusion enthalpy.