Thermodynamic properties and the plastic crystal state of 2-methyl-2-adamantanol

Thermodynamic properties of 1-bromoadamantane in the condensed state and molecular disorder in its crystals

“…In terms of the modified model of plastic crystals [6][7][8], the entropy change and the heat-capacity jump at the ''ordered crystal ! plastic crystal'' transition can be presented in the following manner: FIGURE 4.…”

“…investigations of crystalline adamantane and 1-chloroadamantane [35,36] also point to the onset of rotational motion in their rigid crystals (crII) still well before the transitions to the plastic phases (crI). More justified quantitative calculations according to the model concerned [6][7][8] require a consideration of a transition from an anisotropic ordered crystals (without rotational reorientations of molecules) to a plastic phase (with isotropic molecular rotation). For this purpose, a contribution not connected to the orientational disorder has to be separated from the heat capacity of low-temperature crystals using equations (4) and (5).…”

“…It should be emphasized that the heat-capacity jump was not amenable to theoretical treatment in the context of the earlier Guthrie-McCullough theory [3,5]. The modified model was applied to a number of cage hydrocarbons [6], the presence of hydrogen bonds in the plastic phases for hydroxyl derivatives of adamantane being additionally taken into account [7,8].…”

“…Numbers of non-equivalent orientations of molecules (n orient ) and values of the mean energy differences between ''basic'' and ''plastic'' orientations (D orient H) in isotropic plastic crystals of some adamantane derivatives are estimated according to the modified model of energy states of molecules in plastic crystals [6][7][8]. The trends in the n orient and D orient H values for the series of compounds concerned are analysed.…”

Dynamics of the Crystal to Plastic Crystal Transition in the Hydrogen Bonded N-Isopropylpropionamide

“…13 A weakening of the hydrogen bond strength in the plastic phase has also been deduced from infrared and Raman spectroscopy. 11,14 For example, it was shown that 2-methyladamantanol forms hydrogen bonded dimers in the ordered crystalline state, whereas in the plastic crystal monomers and dimers are in equilibrium. 14 Here the ordered and plastic crystalline phases of NiPPA are characterized by X-ray diffraction and dielectric spectroscopy is used to monitor the changes in molecular rotation with temperature.…”