(E)-3-(4-Chlorophenyl)-2-(2-thienyl)acrylonitrile: chains built from C-H...N hydrogen bonds

The thiophene rings are disordered over two orientations corresponding to a 180 rotation about the C2—C22 bond (Fig. 1); the two conformers have unequal occupancy, with refined site-occupancy factors for the major and minor conformers of 0.802 (3) and 0.198 (3), respectively. The bond distances show no unexpected values; in particular, the C—N and C—C distances for the nitrile unit (Table 1) are typical, where the mean values (Allen et al., 1987) are 1.136 and 1.427 Å, respectively. The bond angles at C2 deviate significantly from regular trigonal geometry, while the C—C—N fragment is not quite linear. While both orientations of the thiophene unit are almost coplanar with the central C C double bond, the 4-chlorophenyl ring is twisted well out of this plane. Thus, the dihedral angles between the plane of the central space unit C22—C2 C3—C31 and the planes of the adjacent rings are as follows: thiophene ring (major orientation) 5.7 (2) , thiophene ring (minor orientation) 4.9 (5) and aryl ring 38.2 (2) . The molecules are linked by a single C—H N hydrogen bond (Table 2) into C(5) (Bernstein et al., 1995) chains generated by the n-glide planes and running parallel to the [101] direction (Fig. 2). Two such chains, related to one another by inversion, pass through each unit cell, but there are no direction-specific interactions between adjacent chains: in particular – stacking interactions, and C—H (arene) and C—H (thiophene) hydrogen bonds are all absent.

In the title compound, C 13 H 8 ClNS, the thiophene ring is disordered over two orientations. The molecules are linked into C(5) chains by a single C-HÁ Á ÁN hydrogen bond.

Comment
The title compound, (I), was prepared for use as an intermediate in the synthesis of new fused heterocyclic systems.
The thiophene rings are disordered over two orientations corresponding to a 180 rotation about the C2-C22 bond (Fig. 1); the two conformers have unequal occupancy, with refined site-occupancy factors for the major and minor conformers of 0.802 (3) and 0.198 (3), respectively. The bond distances show no unexpected values; in particular, the C-N and C-C distances for the nitrile unit (Table 1) are typical, where the mean values (Allen et al., 1987) are 1.136 and 1.427 Å , respectively. The bond angles at C2 deviate significantly from regular trigonal geometry, while the C-C-N fragment is not quite linear. While both orientations of the thiophene unit are almost coplanar with the central C C double bond, the 4-chlorophenyl ring is twisted well out of this plane. Thus, the dihedral angles between the plane of the central space unit C22-C2 C3-C31 and the planes of the adjacent rings are as follows: thiophene ring (major orientation) 5.7 (2) , thiophene ring (minor orientation) 4.9 (5) and aryl ring 38.2 (2) . The molecules are linked by a single C-HÁ Á ÁN hydrogen bond (Table 2) into C(5) (Bernstein et al., 1995) chains generated by the n-glide planes and running parallel to the [101] direction (Fig. 2). Two such chains, related to one another by inversion, pass through each unit cell, but there are no direction-specific interactions between adjacent chains: in particularstacking interactions, and C-HÁ Á Á(arene) and C-HÁ Á Á(thiophene) hydrogen bonds are all absent.

Experimental
A solution of 2-thiopheneacetonitrile (2.87 mmol) and potassium tertbutoxide (0.53 mmol) in anhydrous ethanol (3 ml) was stirred at room temperature for 15 min; a solution of 4-chlorobenzaldehyde (2.87 mmol) in anhydrous ethanol (3 ml) was then added. The resulting precipitate was collected by filtration, washed with ethanol, dried and finally crystallized from dimethylformamide to give yellow crystals suitable for single-crystal X-ray diffraction.  Table 1 Selected geometric parameters (Å , ).
All H atoms were located in difference maps and then treated as riding atoms, with C-H = 0.95 Å and U iso (H) = 1.2U eq (C). It was apparent at an early stage that the thiophene unit was disordered over two sets of sites related by a rotation of 180 about the exocyclic C-C bond; the geometry of the minor orientation was restrained to match that of the major orientation, and the anisotropic displacement parameters for corresponding atoms in the two orientations were constrained to be equal. The deepest hole in the difference map is located 0.33 Å from the minor-occupancy atom S21A.

Figure 1
The molecule of compound (I), showing the atom-labelling scheme for (a) the major conformer and (b) the minor conformer. Displacement ellipsoids are drawn at the 30% probability level.