The Crystal Structure of Octyl-D-gluconate: A Mesogenic Structure with Monolayer Head-to-Tail Molecular Packing

Abstract

Octyl-D-gluconate, C₁₄H₂₈O₇, is monoclinic, P2₁, Z = 2, a = 4.798(1), b = 32.353(8), c = 5.241(1) Å, β = 94.90(1)° at room temperature. On heating, the crystal undergoes three crystal-to-crystal transitions, two at 62 to 67°C and a more pronounced one at 90°C. Melting to a liquid crystal smectic phase takes place at 158°C, which melts again within one degree to an isotropic liquid. On cooling, the liquid crystal phase is metastable to 110°, when crystallization takes place through four crystal phases down to room temperature, In the room temperature crystal structure, both the acyclic gluconate moiety and the alkyl chains are in the extended conformation. The gluconate moieties are hydrogen bonded. The molecular packing in monolayer and head-to-tail, in contrast to the bilayer head-to-head packing of the long chain alkyl carbohydrates having cyclic sugar residues. The alkyl chains are aligned parallel with no intercalation.