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

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°.