Monoclinic polymorph of 2,5-dide-oxy-2,5-epithio-1,3:4,6-bis-O-[(R)-phenyl-methyl-ene]-l-iditol

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The title compound C(20)H(20)O(4)S, is polymorphic. In the tetra-gonal form, the mol-ecule lies on a crystallographic twofold axis, while the monoclinic form has only approximate C(2) mol-ecular symmetry. The greatest excursion from C(2) symmetry is in the orientation of the two phenyl rings; at 100 K, one of the rings is rotated -37.2 (3)° and the other by 46.9 (3)° from their symmetric (tetra-gonal) positions. There are only minor differences in the three-ring nucleus; the best mol-ecular fit of the tetra-gonal and monoclinic forms, both at 100 K and excluding phenyl rings and H atoms, shows an r.m.s. deviation of 0.066 Å. Both forms have the same absolute configuration.

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Acta crystallographica. Section E, Structure reports online

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