The Space-Group and Molecular Symmetry of Beta-Benzenehexabromide and Hexachloride

The small crystallographic symmetry of most organic compounds has limited the determination of their structures by crystal-structure researches. Yet many problems of structural organic chemistry can be so answered. We have determined the space-group and molecular symmetry of β-benzene hexabromide and hexachloride, and have obtained information of value in the interpretation of the geometrical isomerism of these compounds. Both benzene hexabromide, C6H6Br6 and benzene hexachloride, C6H6Cl6, crystallize in two modifications differing markedly in physical properties. The monoclinic forms, designated alpha, have been assigned the "trans" configuration. The "cis" or beta modification of the hexabromide crystallizes in the cubic system, while the hexachloride has been reported to form hexagonal crystals which are pseudocubic. Our investigation has been restricted to the beta forms.