One mol­ecule, three crystal structures: conformational trimorphism of N-[(1S)-1-phenyl­eth­yl]benzamide

The title compound, C(15)H(15)NO, 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 P2(1) and P2(1)2(1)2(1). 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 C (1) (1)(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 P2(1) in forms I and II, respectively. As for form III, the asymmetric unit contains two independent mol­ecules forming parallel chains in space group P2(1)2(1)2(1), and the crystal structure combines features of monoclinic forms I and II.