4-Methoxybenzenecarbothioamide

The asymmetric unit of the title compound, C8H9NOS, contains two independent molecules with the methoxy groups oriented in opposite conformations. The mean planes of the carbothioamide groups are tilted by 7.88 (15) and 11.16 (9)° from the mean planes of the benzene rings. In the crystal, the molecules form dimers via intermolecular N—H⋯S intermolecular hydrogen bonds, resulting in eight-membered rings of R 2 2(8) graph-set motif. The dimers are further linked by C—H⋯O hydrogen bonds into chains along the c axis. Adjacent chains interact through intermolecular N—H⋯S hydrogen bonds, generating eight-membered rings of R 4 2(8) graph-set motif.

The asymmetric unit of the title compound, C 8 H 9 NOS, contains two independent molecules with the methoxy groups oriented in opposite conformations. The mean planes of the carbothioamide groups are tilted by 7.88 (15) and 11.16 (9) from the mean planes of the benzene rings. In the crystal, the molecules form dimers via intermolecular N-HÁ Á ÁS intermolecular hydrogen bonds, resulting in eight-membered rings of R 2 2 (8) graph-set motif. The dimers are further linked by C-HÁ Á ÁO hydrogen bonds into chains along the c axis. Adjacent chains interact through intermolecular N-HÁ Á ÁS hydrogen bonds, generating eight-membered rings of R 4 2 (8) graph-set motif.

Comment
Thioamides exhibit a wide range of applications, not only as synthetic intermediates in the synthesis of a variety of heterocyclic compounds (Zahid et al., 2009), but also numerous biological activities have been associated with them (Jagodzinski, 2003;Klimesova et al., 1999). Moreover, thioamides are important ligands in the field of coordination chemistry (Lebana et al., 2008). In continuation to our work on thioamides (Khan et al., 2009a;2009b;2009c), we have synthesized 4-methoxybenzothioamide. In this article we report the crystal structure of the title compound.
The title structure contains two conformational isomers, molecule A and B, containing atoms S1 and S11, respectively, in an asymmetric unit with methoxy groups oriented in opposite conformations (Fig. 1). The mean-planes of the carbothioamide groups (S/N/C) are tilted by 7.88 (15) and 11.16 (9)° from the mean-planes of the phenyl rings in molecules A and B, respectively. The dihedral angle between the mean-planes of the phenyl rings of the two molecules is 58.57 (4)°. The molecules A and B form dimers via N-H···S type intermolecular hydrogen bonds resulting in eight membered rings in R 2 2 (8) motif (Bernstein et al., 1994). The dimers are further linked by C8-H8B···O11 hydrogen bonds into chains along the c-axis (Fig. 2). The adjacent chains of molecules are held together by N-H···S type intermolecular hydrogen bonds resulting in eight membered rings in R 4 2 (8) motif (Fig. 3); details of hydrogen bonding geometry have been provided in Table 1.
The bond distances and angles in both molecules agree with the cortresponding bond distances and angles reported in closely related compounds (Khan et al., 2009a;2009b;2009c;Jian et al., 2006).

Experimental
A slurry of magnesium cholride hexahydrate (5.8 mmol) and sodium hydrogen sulphide hydrate (70%, 11.6 mmol) was prepared in dimethylformamide (15 ml). 4-Methoxybenzonitrile (5.8 mmol) was added to the slurry and the reaction mixture was stirred at room temperature for 5 h. The reaction mixture was poured into water (60 ml) and the resulting precipitates were collected by filtration. The product obtained was resuspended in 1 N HCl (30 ml), stirred for another 25 min, the precipitated solid filtered and washed with water. Recrystallization of the product from chloroform afforded the crystals of the title compound suitable for X-ray crystallographic analysis.

Refinement
Though all the H atoms could be distinguished in the difference Fourier map the H-atoms bonded to C-atoms were included at geometrically idealized positions and refined in riding-model approximation with C-H = 0.95 and 0.98 Å for aryl and methyl H-atoms, respectively. The H-atoms bonded to N atoms were allowed to refine. The U iso (H) were allowed at 1.2/1.5U eq (N/C). The final difference map was essentially featurless.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.