Thermodynamic properties and phase transitions of 1-methylcyclohexanol and 1-chloro-1-methylcyclohexane

Comprehensive investigations of thermodynamic properties of 1-methylcyclohexanol (I) and 1-chloro-1-methylcyclohexane (II) were carried out. The heat capacities and enthalpies of transitions of I and II in the condensed state between 5 and 320 K were measured by vacuum adiabatic calorimetry. It was found that II exists in the plastic crystal state over a narrow temperature interval from 214.37 to 234.52 K. The enthalpies of sublimation of I and vaporization of II and their saturated vapor pressures were obtained. Infrared (LR) and Raman spectra of both compounds were recorded and vibrational analyses were made. Thermodynamic functions of I and II in the ideal gas state were calculated by the statistical thermodynamics methods. It was shown by the low-temperature LR spectroscopy that only one 'chair'-conformer of II with equatorial methyl group exists in rigid crystal phase at T<214.37 K. The nature of molecular rotation in the plastic crystal state of II is discussed. (C) 1998 Elsevier Science B.V.