The title compound, C15H15NO, is an enantiopure small molecule, which has been synthesized many times, although its crystal structure was never determined. By recrystallization from a variety of solvent mixtures (pure acetonitrile, ethanol–water, toluene–ethanol, THF–methanol), we obtained three unsolvated polymorphs, in space groups P21 and P212121. Form I is obtained from acetonitrile, without admixture of other forms, whereas forms II and III are obtained simultaneously by concomitant crystallizations from alcohol-based solvent mixtures. All forms share the same supramolecular structure, based on infinite C11(4) chain motifs formed by N—H...O intermolecular hydrogen bonds, as usual for non-sterically hindered amides. However, a conformational modification of the molecular structure, related to the rotation of the phenyl rings, alters the packing of the chains in the crystal structures. The orientation of the chain axis is perpendicular and parallel to the crystallographic twofold screw axis of space group P21 in forms I and II, respectively. As for form III, the asymmetric unit contains two independent molecules forming parallel chains in space group P212121, and the crystal structure combines features of monoclinic forms I and II.
Cocrystallization experiments of the cyclic amides (lactams) 1,4-dihydroquinoxaline-2,3-dione (DHQ) and 1H-benzo[d]imidazol-2(3H)-one (BIM) with the anilic acids 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (CA) and 2,5-dihydroxy-1,4-benzoquinone (AA) yielded a total of five cocrystals and cocrystal hydrates,...
The title salt, C14H14N3O4S2
+·Cl− [systematic name: 2-(4-hydroxy-2-methyl-1,1-dioxo-1,2-benzothiazine-3-amido)-5-methyl-1,3-thiazol-3-ium chloride] is the hydrochloride derivative of meloxicam, a drug used to treat pain and inflammation in rheumatic disorders and osteoarthritis. Although its molecular structure is similar to that previously reported for the hydrobromide analogue, both salts are not isomorphous. Different crystal structures originate from a conformational modification, arising from a degree of rotational freedom for the thiazolium ring in the cations. By taking as a reference the conformation of meloxicam, the thiazolium ring is twisted by 10.96 and −16.70° in the hydrochloride and hydrobromide salts, while the 1,2-benzothiazine core is a rigid scaffold. This behaviour could explain why meloxicam is a polymorphous compound.
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