Crystal structures and thermal analyses of alkyl 2-deoxy-alpha-d-arabino-hexopyranosides.

The crystal structures of alkyl 2-deoxy-alpha-d-arabino-hexopyranosides, with the alkyl chain lengths from C(8) to C(18), are established by the single crystal X-ray structural determination. The even-alkyl chain length derivatives crystallized orthorhombic, with space group P2(1)2(1)2(1), whereas the odd-alkyl chain length derivatives crystallized monoclinic, with space group P2(1). The sugar moieties retained a (4)C(1) chair conformation and the conformation of the alkyl chains was all-trans. The molecules formed a bilayer structure, in which alkyl chains were interdigitated. The hydrogen bonds, originating from the sugar moieties, were observed in adjacent layers and also within the same layer, resulting in the formation of infinite chains. The alkyl chains arranged parallel to each other and formed planar structures. The thermal properties of the alkyl 2-deoxy glucosides were analyzed further. It was observed that none of the derivatives exhibited mesomorphism. This study establishes that the absence of the hydroxyl group at C-2 of the sugar moiety results in a non-mesogenic nature of the alkyl 2-deoxy-alpha-d-glycosides, as opposed to the profound mesogenic nature of the normal alkyl glycosides.