The thermodynamics of orientational disorder in a molecular solid: (CH₃)₃CCHO

Abstract

This paper is dedicated to Professor James A. Morrison MARY ANNE WHITE and ALLYSON PERROTT. Can J. Chem. 66, 729 (1988) The heat capacity of tert-butylaldehyde, (CH3)3CCH0, has been measured as a function of temperature from 29 to 298 K, to investigate solid-state polymorphism. There are two solid-solid phase transitions in this material, T,, = 158.5 and 183.9 K, AS,, = 0.402R and 3.153R respectively. The thermodynamic parameters for the transitions are consistent with mechanisms proposed on the basis of recent nuclear magnetic resonance investigations of this material.MARY ANNE WHITE et ALLYSON PERROTT. Can J. Chem. 66, 729 (1988) Afin d'ttudier le polymorphisme a l'ttat solide, on a mesurt la capacitt calorifique du tert-butylaldthyde, (CH3)3CCH0, en fonction de la temptrature de 29 a 298 K. Avec ce produit, on a observt deux transitions de phase solide-solide, T,, = 158,5 et 183,9 K, AS,, = 0,402R et 3,153R. Les paramktres thermodynamiques pour les transitions sont en accord avec les mtcanismes proposts en se basant sur des etudes rtcentes en resonance magnttique nucltaire de ce compost.[Traduit par la revue]

A thermodynamic investigation of dynamical disorder in Phase II of CBr4

“…On this basis it is clear why the NMR experiment 13 detected significant molecular motion in phase II. Whereas in some molecular solids NMR results can indicate pretransitional effects far below the temperature of the phase transition, 31,32 this appears not to be the case here; the detected motion is an intrinsic feature of phase II of CBr 4 . Although thermal conductivity results for phase II of CBr 4 have been interpreted in terms of structural disorder, 14 it would appear that the structure is ordered but the rotationalvibrations of the molecules are fully excited at relatively low temperatures.…”

Dynamics of anions and cations in cesium hydrogensulfide (CsHS, CsDS): Neutron and x-ray diffraction, calorimetry and proton NMR investigations

“…However, the calorimetric investigations indicate that this is not due to an intrinsic difference between CsHS and CsDS. On the one hand, the difference could be related to the difference in sensitivity of different techniques to different aspects of dynamics 41,42. On the other hand, there might be an influence of an amorphous phase, as mentioned in Ref 8…”