CONFORMATIONAL POLYMORPHISM OF D-SORBITOL (D-GLUCITOL) - THE CRYSTAL AND MOLECULAR-STRUCTURES OF D-GLUCITOL 2 3-HYDRATE AND EPSILON-D-GLUCITOL/

The crystal structures of D-glucitol 2/3-hydrate (1) and epsilon D-glu citol (2) were determined by X-ray crystallography and refined to fina l conventional parameters of R = 0.034 and 0.050, respectively. The co nformations of the three independent molecules of 1 and one of the two independent molecules of 2 are similar and exhibit, bent-chain, sickl e conformations of the carbon chain, thus avoiding the unfavourable 1, 3-parallel O//O interactions. However, the orientation of a terminal h ydroxyl group differs from the one observed in the bent-chain conforma tion of the known A form. An even more striking observation is the une xpected, extended, zigzag conformation of the second independent molec ule of 2, which results in a 1,3-parallel interaction between O-2 and O-4. Thus in the class of alditols, the crystals of the epsilon and A forms of D-glucitol constitute the rarely occurring type of conformati onal polymorphism. (C) 1998 Elsevier Science Ltd. All rights reserved.