Orientational order in two-component plastic crystals 2,2-dichloropropane–carbon tetrachloride

Abstract

1H nuclear magnetic resonance (NMR) spectra and birefringence of noncubic plastic single crystals (CH3)2CCl2–CCl4 have been measured. The investigation has demonstrated that in these crystals weak preferred orientations of molecules were observed. Concentration dependence of orientational ordering matrix of (CH3)2CCl2 molecules has been obtained from computer simulations of NMR line shape and birefringence data. It has been found that all ordering matrix elements become zero at mole fraction of 2,2-dichloropropane 0.5.

Multiple melting of orientationally disordered mixed crystals of the two-component system (CH3)2CCl2–(CH3)CCl3

“…1,2 The lattice symmetry of stable phase Ib was determined as rhombohedral (R, Z ¼ 21) on the basis of X-ray powder diffraction experiments and from the optical examination of the crystals which revealed the phase as birefringent. [19][20][21]24,25 The OD R stable phase melts at 236.6 K. 1,2,7,10 In relation to the OD metastable phase Ia, although the patterns were tentatively indexed according to a face centered cubic (FCC, Z ¼ 4) lattice, 26 a recent work has established that this phase displays a simple cubic (SC, Z ¼ 20) symmetry. 10 This phase melts at 230.4 K. The structure of the low-temperature ordered phase (II), which transforms to the OD R phase at 187.8 K, has been recently determined as monoclinic (C2/c, Z ¼ 4).…”

“…2,5 Several twocomponent systems relating to such compounds have been carefully studied. 5,[7][8][9]11,12,[19][20][21] Particularly, the analysis of the two-component systems (CH 3 ) 2 CCl 2 + CCl 4 7 and (CH 3 )CCl 3 + CCl 4 5 has demonstrated a isomorphism relationship between the stable OD rhombohedral phases. Thus, a continuous formation of mixed crystals in the 2,2-dichloropropane ((CH 3 ) 2 -CCl 2 ) + methylchloroform ((CH 3 )CCl 3 ) two-component system studied in this work, is expected.…”

On the Crystallography and Thermodynamics in Orientationally Disordered Phases in Two-Component Systems

“…At a given temperature ¹, the relation [7] can be directly derived from expressions [6a] and [5]. Exact excess enthalpy data are rather difficult to obtain.…”

“…Another powerful way to modify the molecular surroundings is to introduce a foreign substance (6)(7)(8). In experimental practice this comes down to the study of binary systems.…”

Analysis of the Heat Capacity for Pure CH4 and CH4/CCl4 on Graphite Near the Melting Point and Calculation of the T–X Phase Diagram for (CH3)CCl3+CCl4

“…Both OD phases, namely, stable (rhombohedral) and metastable (face-centered cubic, FCC) phases have been studied by the measurements of optical birefringence [25], Raman [26], and Brillouin scattering [27,28]. Birefringence measurements have also been conducted for the mixed non-cubic orientationally disordered (OD) crystals of CH 3 CCl 3 +CCl 4 [29] and (CH 3 ) 2 CCl 2 +CCl 4 [30]. In particular, for the methyl chloroform-carbon tetrachloride by analyzing the concentration dependence of the birefringence the orientational order parameters of axially symmetric molecules have been calculated in this two-component plastic crystal [29].…”