The low-temperature heat capacity and the thermodynamic functions of 1,3,5-trimethyladamantane

The heat capacity of 1,3,5-trimethyladamantane was measured in the temperature range 7.9-356 K by the method of adiabatic calorimetry. An order-disorder solid-state transition was observed. The temperatures, enthalpies, and entropies of the solid state transition and fusion were determined; according to the melting point curves, the sample was 99.98 mol % pure. The conclusion of the formation of plastic crystals in the high-temperature phase of 1,3,5-trimethyladamantane was drawn. The {S-m(o)(T) - S-m(o)(0)}, {H-m(o)(T) - H-m(o)(0)}, and -{G(m)(o)(T) - H-m(o)(0)} thermodynamic functions and the entropy of formation in the ideal gas state at 298.15 K were calculated.