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Phase transitions in the crystalline state of chiral sorbose were examined using precise heat capacity calorimetry and X-ray crystallography. The calorimetry established heat capacity below room temperature. Besides the known transition (main transition) at 199.5 K, the calorimetry detected plural thermal anomalies assignable to new phase transitions (around 210 K) and a glass transition (at ca. 120 K). The X-ray diffraction at low temperatures established the crystal structure of the lowest temperature phase. The identification of the broken symmetry upon the main transition solves an apparent contradiction that the structural disorder reported previously does not contribute seemingly to the symmetrization.

Heat capacities of the plastic crystal formylferrocene have been measured with adiabatic calorimetry in the 13-405 K temperature region. Three phase transitions hitherto reported were observed at 293.53 K (second-order phase transition), 317.03 K (first-order phase transition to plastic crystal phase), and 397.60 K (fusion). The enthalpy and entropy of transition were determined as ΔH = (0.887 ± 0.01) kJ mol-1/ΔS = (3.39 ± 0.05) J K-1 mol-1, (13.29 ± 0.01) kJ mol-1/(42.10 ± 0.01) J K-1 mol-1, and 2.76 kJ mol-1/6.88 J K-1 mol-1, respectively. Mechanisms governing the phase transitions are discussed. Because formylferrocene has an almost spherical molecular structure, it can reorient quasi-isotropically in the solid state. This situation bears a close resemblance to that encountered in fullerene C60. [ABSTRACT FROM AUTHOR]

Heat capacity of ZrW2O8 was measured in the (1.8 to 483) K temperature range by using two adiabatic and a commercial relaxation calorimeters. Standard thermodynamic functions of ZrW2O8 were estimated from the measured molar heat capacity. A large λ-type anomaly of heat capacity due to an order–disorder phase transition was observed at T=(440±0.5) K. The enthalpy and entropy of phase transition were determined to be (1.56 ± 0.01) kJ · mol−1 and (4.09 ± 0.03) J · K−1 · mol−1, respectively. The magnitude of the entropy of transition supports the order–disorder mechanism previously suggested by the present authors. [Copyright &y& Elsevier]

Meaning of the alkyl chain-length dependence of transition entropy in liquid crystal is discussed and clarified in a long-chain region. A method to deduce contributions of the alkyl chain and the molecular core is proposed. Application of the method suggests that, in most smectic A (SmA) - nematic (N) phase transitions, not only a molecular core (modeled by a hard-rod) but also a (terminal) alkyl chain is disordered upon the SmA→N transition. [ABSTRACT FROM AUTHOR]

Phase transitions in the crystalline state of chiral sorbose were examined using precise heat capacity calorimetry and X-ray crystallography. The calorimetry established heat capacity below room temperature. Besides the known transition (main transition) at 199.5 K, the calorimetry detected plural thermal anomalies assignable to new phase transitions (around 210 K) and a glass transition (at ca. 120 K). The X-ray diffraction at low temperatures established the crystal structure of the lowest temperature phase. The identification of the broken symmetry upon the main transition solves an apparent contradiction that the structural disorder reported previously does not contribute seemingly to the symmetrization. [ABSTRACT FROM AUTHOR]