Differential Thermal Analysis and Dielectric Studies on Neopentanol under Pressure

Abstract

Differential thermal analysis (DTA) and dielectric measurements have been performed on 2,2-dimethyl- 1-propanol (neopentanol) up to 200 MPa. Neopentanol exhibits at least one orientationally disordered (ODIC) phase (solid I) that transforms at lower temperatures to a non-plastic phase (solid II). There is evidence of a further ODIC phase denoted as solid I'. The pressure dependence of the phase transitions and the dielectric behaviour up to frequencies of 13 MHz are described. Activation enthalpies and volumes are derived from the dielectric relaxation time and compared with results for other alcohols

Dielectric spectroscopy on two orientationally disordered crystals: NPA (CH2OHC(CH3)3) and TCE (CH2OHCCl3)

“…The existence of two stable and structurally different solid forms has been established: a low-temperature ordered state (form II) which recently has been determined to be triclinic [9]-stable up to 235.4 K-and an ODIC state (form I), the structure of which is face centred cubic (probably F m3m) [7]-stable up to the melting point at 329.8 K. Nevertheless, Würflinger and co-workers in a relatively recent study of differential thermal analysis (DTA) and dielectric spectroscopy under pressure, showed the possible existence of two ODIC states. The transition between them was observable in the static permittivity measurements but not in the DTA measurements [3]. On the other hand, a recent x-ray powder diffraction study [5] has shown the next behaviour.…”

“…Likewise, it may be underlined that the chlorine atom has practically the same volume as the methyl group. Up to date, experimental dielectric studies on tetrahedral molecular compounds closely related to the above-mentioned are rather scarce [1][2][3][4]. The fundamental reason for this fact is probably a relatively high frequency domain for the dielectric losses.…”

“…As far as NPA is concerned, differential thermal analysis by DSC [3,5], NMR [6], x-ray powder diffraction [5,[7][8][9], static dielectric permittivity at normal pressure and complex permittivity under pressure [3] have been studied in the last 30 years, making evident its particular polymorphism. The existence of two stable and structurally different solid forms has been established: a low-temperature ordered state (form II) which recently has been determined to be triclinic [9]-stable up to 235.4 K-and an ODIC state (form I), the structure of which is face centred cubic (probably F m3m) [7]-stable up to the melting point at 329.8 K. Nevertheless, Würflinger and co-workers in a relatively recent study of differential thermal analysis (DTA) and dielectric spectroscopy under pressure, showed the possible existence of two ODIC states.…”

Thermal and Structural Characterization of (CH3)3CCl

“…2-Chloro-2-methyl-propane, (CH 3 ) 3 CCl or tert -butyl-chloride (TBCl), belongs to a group of molecular compounds of common chemical structure, (CH 3 ) 3 CX. For a large number of substituents X, the existence of an orientationally disordered phase has been found (X = Br, I, CN, SH, NO 2 , CH 3 , NH 2 , COOH, CH 2 OH, and so on). − Many detailed studies of the molecular motions in the solid phases of tert -butyl compounds have been performed using neutron scattering, − dielectric, − NMR, − and, to a lesser extend, X-ray diffraction − techniques. The results of these measurements have enabled researchers to better characterize the dynamics and the thermodynamics of the ordered and disordered phases.…”

Differential Thermal Analysis and Dielectric Studies on 2-Methyl-2-Nitro-Propane under High Pressure

“…The experimental devices for the high-pressure DTA [18,19] and the dielectric measurements [13,20,21] have been described previously. We employed a Hewlett Packard 4192 A impedance analyser that al lowed to vary the frequency up to 13 MHz.…”