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-nitrobenzenethialato)-2-phenylethene, C15H13NO2S (1) ( orthorhombic Pbca), the nitro group is almost coplanar with the adjacent ar yl ring, but the dihedral angles between the nitro-aryl and styryl fragment s is similar to 121. The molecules are linked by paired C--H ... O hydrogen bonds in a chain of rings In S-(2-nitrophenyl)benzene-carbothiolate, C13H9 NO3S (2) (monoclinic P2(1)/a), the nitro group is rotated by 33.0 (2)degree s 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 mo lecules or (2) are linked into chains by C--H ... O hydrogen bonds, and eac h chain is linked to two neighbouring chains by means of aromatic pi...pi s tacking interactions. In 1-(2-nitrophenylthio)2,5-pyrrolidinedione, C10H8N2 O4S (3) (monoclinic P2(1)la), 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 calculat ions 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 molec ules of (2) adopt a conformation in the crystal close to that calculated fo r the local energy minimum, Comparisons are made with the structures of som e related compounds and it is concluded that, while the nature of the two c onformational minima is determined by intramolecular forces, the choice bet ween them is determined primarily by intermolecular forces.