The Crystal Structure of Octyl-1-thio-β-D-xylopyranoside: A Disordered Smectogenic Structure

Octyl-l-thio-β-D-xylopyranoside, C13H26O4S, forms a mesophase at 373 K and melts at 387 K, with an intermediate solid-to-solid phase transition at 330 K. The structure is disordered at 293 K and remains so at 123 K. The average room temperature [low temperature] crystal structure, at 293 K [123 K], is orthorhombic P212121, Z = 4, with a = 7.675(2) [7.597(3)], b = 4.830(9) [4.762(1)], c = 40.954(7) [40.828(9)] Å, V = 1518.2 [1447.0] Å3, Dx = 1.216 g cn−3, Dm = 1.218 g cm −3. The average structure was solved using MULTAN and refined on 1356 [1573] observations to R = 0.059 [0.040], Rw = 0.066 [0.059]. The disorder is in the carbohydrate moiety, which has two orientations with equal occupancy. The intercalated alkyl chains are ordered. The diffuse diffraction corresponds to a super lattice a, 2b, 2c, with a periodic variation along b.