Polymorphism of the Crystalline Methylchloromethane Compounds. IV. The Crystal and Molecular Structure of Methyl Chloroform at −60° and −145°

Abstract

The crystal structure of the ordered form of solid methylchloroform (1,1,1-trichloroethane) has been determined from three-dimensional x-ray film data, collected at −60° and −145°. The data revealed no significant structural differences between the solids at these temperatures. The existence of a crystal-lographic phase transition at −68° is thus ruled out. The crystals are orthorhombic, space group, Pnma, with four molecules per unit cell. The lattice dimensions are a=11.53(1) Å, b=8.000(5) Å, c=5.88(1) Å at −60° and a=11.46(1) Å, b=7.890(5) Å, c=5.81(1) Å at −145°. The C–Cl distance is 1.782(16) Å. Analysis of the thermal parameters indicate that at −60° there is a greater degree of librational motion about the C–C axis than at −145°.

Polymorphism of 2,2-Dichloropropane: Crystallographic Characterization of the Ordered and Disordered Phases

“…As far as the molecular structure is concerned, the bond lengths and angles obtained after refinement are collected in Table . The C−Cl bond has been reported in compounds similar to CH 3 Cl (1.778 Å) and to the homologous compounds (CH 3 )CCl 3 (1.775 Å) and (CH 3 ) 3 CCl (1.81 Å). , The C−C distance compares also favorably with the accepted values and with those of similar molecules (1.548 Å for (CH 3 )CCl 3 32 and between 1.53 and 1.57 Å for (CH 3 ) 3 CCl 7,33 ). With regard to the angles involving the central carbon atom, the C−C−C angle (110.9°) is slightly larger than the average value of the C−C−Cl angles (109.5°) and noticeably larger than the Cl−C−Cl angle (107.8°), although close values were obtained for (CH 3 )CCl 3 and (CH 3 ) 3 CCl (C−C−C, 109.5° and 111.1°; C−C−Cl, 110.2° and 107.9° ; Cl−C−Cl, 108.8°).…”

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

“…(CH 3 )CCl 3 displays a polymorphism consisting of two stable and one metastable forms in the solid state. 2,5,12,26 The phase behavior of (CH 3 )CCl 3 can be summarized as follows: At 224.0 K it transforms from an ordered low-temperature solid form (Pnma, Z ¼ 4), 28 to the Ib OD form (rhombohedral, Z ¼ 21) which is stable up to the melting point at 241.9 K. When cooling from the liquid state the monotropic phase Ia (which has a FCC symmetry and Z ¼ 4) crystallizes and a subsequent heating gives rise to the melting at 235.8 K. The characteristic temperatures and enthalpy changes associated with the described transitions are gathered in Table 1 and agree with the published data. 1,29 Cubic symmetry was early assigned to the OD stable phase of (CH 3 )CCl 3 according to X-ray powder diffraction experiments as well as optical examination of the crystals.…”

Stable and Metastable Phase Diagram of the Two-Component System (CH3)3CCl−(CH3)CCl3: An Example of Crossed Isodimorphism

“…(CH 3 )CCl 3 (1,1,1-Tricloroethane or Methylchloroform). At 224.0 K (CH 3 )CCl 3 transforms from an ordered low-temperature solid form (denoted as O) to the Ib OD form, which is stable up to the melting point at 241.9 K. The symmetry of the low-temperature ordered phase is known to be orthorhombic ( Pnma ). , …”