Monoclinic polymorph of 2,5-dideoxy-2,5-epithio-1,3:4,6-bis-O-[(R)-phenylmethylene]-l-iditolCAS: 151061-72-2.

The title compound C20H20O4S, is polymorphic. In the tetragonal form, the molecule lies on a crystallographic twofold axis, while the monoclinic form has only approximate C2 molecular symmetry. The greatest excursion from C2 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 (tetragonal) positions. There are only minor differences in the three-ring nucleus; the best molecular fit of the tetragonal 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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