Conformational preferences in 2-nitrophenylthiolates: interplay between intra- and intermolecular forces; structures of (E)-1-(4-methyl-2-nitrobenzenethiolato)-2-phenylethene, S-(2-nitrophenyl)-benzenecarbothiolate and 1-(2-nitrophenylthio)-2,5-pyrrolidinedione

In (E)-1-(4-methyl-2-nitrobenzenethiolato)-2-phenylethene, C15H13NO2S (1) (orthorhombic Pbca), the nitro group is almost coplanar with the adjacent aryl ring, but the dihedral angles between the nitro-aryl and styryl fragments is approximately 121 degrees. The molecules are linked by paired C-H...O hydrogen bonds in a chain of rings. In S-(2-nitrophenyl)benzenecarbothiolate, C13H9NO3S (2) (monoclinic P2(1)/a), the nitro group is rotated by 33.0 (2) degrees out of the plane of the adjacent aryl ring and the thiobenzoate group is strongly twisted away from the plane of the disubstituted aryl ring. The molecules of (2) are linked into chains by C--H...O hydrogen bonds, and each chain is linked to two neighbouring chains by means of aromatic pi... pi stacking interactions. In 1-(2-nitrophenylthio)-2,5-pyrrolidinedione, C10H8N2O4S (3) (monoclinic P2(1)/a), the nitro group is again almost coplanar with the adjacent aryl ring, but the pyrrolidinedione unit is almost orthogonal to the O2NC6H4SN plane. There are three types of C-H...O hydrogen bond in the structure, and these link the molecules into a two-dimensional net. The conformations of these molecules have been investigated by SCF calculations and two energy minima have been identified for each: the molecules of (1) and (3) adopt conformations in their crystals which are close to those at the overall energy minima calculated for isolated molecules, while molecules of (2) adopt a conformation in the crystal close to that calculated for the local energy minimum. Comparisons are made with the structures of some related compounds and it is concluded that, while the nature of the two conformational minima is determined by intramolecular forces, the choice between them is determined primarily by intermolecular forces.