Contribution of Hydrogen Bonds to Equilibrium αβ Transition of Resorcinol

The equilibrium αβ transition temperature, Tαβ, between the α crystalline phase and the β crystalline phase of resorcinol has been determined when both supercooling and superheating effects vanished. The latent volume and dTαβ/dP have been determined by use of a precision pycnometer, and the thermodynamic characteristics of the αβ transition are presented. The P−V−T relations of each phase have also been obtained. All of the thermal expansion coefficient, the isothermal compressibility, and the internal pressure for the higher-temperature, higher-density polymorph, the β crystal, are much larger than those for the lower-temperature, lower-density polymorph, the α crystal. Contributions of the hydrogen bonds and the van der Waals energy to the internal energy have semiquantitatively been analyzed by use of a simple potential model. When the α crystal transforms to the β crystal, the energy of hydrogen bonds decreases due to the breakdown of the hydrogen bonds, whereas the van der Waals energy increases wit...