Correlations Orientationnelles dans les Dérivés Hexasubstitués du Benzène

Abstract

-X-ray diffuse scattering experiments performed on hexasubstituted benzene derivatives give evidence of a somewhat disordered structure characterized by a strongly anisotropic local order with linear correlation chains parallel to the b axis. In the case of hexachlorobenzene, the chlorine atoms are displaced above and below the ring plane: for superposed molecules the displacements are cooperative and the order extends on a range of about 5 mol. There is no correlation between neighbouring rings in a (a, c) plane. In the high temperature disordered phase of the chloromethyl derivatives, the molecules reorient about their pseudo-sixfold axis and there is no long range order in the distribution of the chlorine and methyl groups. Nevertheless a local antiferroelectric order exists for rings superposed along the b direction. Moreover, as in the case of hexachlorobenzene, the substituted atoms are displaced out of the ring plane.