Thermodynamics Research Center / ThermoML | Thermochimica Acta

ABSTRACT

The NMR study revealed that the 60deg reorientational jumps in non-polar crystalline benzene do not give to a new configuration, and therefore benzene behaves as orientationally ordered system from thermodynamic perspective. All the non-polar symmetric crystalline hexa-substituted benzenes, such as hexachlorobenzene, hexamethylbenzene, etc., are supposed to be characteristically similar like benzene. We selectively probed solid solutions of these non-polar crystalline matrices with polar crystalline species employing dielectric spectroscopy, and differential scanning calorimetry. An additional process, close to Debye in nature, was observed in dielectric spectroscopy with higher activation energy, which was absent in NMR, and based on spectral behaviour we designate it as a-relaxation. Moreover, the single strong process that appears in NMR study of non-polar benzene, hexachlorobenzene, and hexamethylbenzene matrices is identical to a relatively weak process observed in dielectric spectroscopy, which we designate as secondary relaxation. In all the cases, the temperature dependence of the relaxation rates follow Arrhenius equation.