NEW DATA ON HYPERSYMMETRY AND PSEUDOSYMMETRY OF ORGANIC CRYSTALS

The crystal structures of D,L-methylsuccinic acid (I), cyclopropane-1,1-dicarboxylic acid (II), and 2-nitroso-4-methyl-N-aniline (III) [triclinic system the purpose of further investigation of hypersymmetry and pseudosymmetry effects in organic crystalline substances using Cambridge Crystallographic Database. For compound I, its monoclinic modification [P21, Z=4(12)] is additionally examined. Hypersymmetry planes mp are found in all of these substances. For the two modifications of I, the appearance of the hyperplanes mp is dictated by the most advantageous mode of linking of molecular chains. In crystals II, the hyperplanes result from the perturbation of the potential function due to superposition of pseudosymmetric chains with 21 axes. In the case of III, the reason for hypersymmetry is not clear.