2-[(4-Chlorophenyl)sulfanyl]-2-methoxy-1-phenylethan-1-one: crystal structure and Hirshfeld surface analysis

A chiral methine-C atom connects the (4-chlorophenyl)sulfanyl, benzaldehyde and methoxy residues in the racemic title compound. Supramolecular helical chains are formed in the crystal, being sustained by methyl- and methine-C—H⋯O(carbonyl) interactions.

The title compound, C 15 H 13 ClO 2 S, comprises (4-chlorophenyl)sulfanyl, benzaldehyde and methoxy residues linked at a chiral methine-C atom (the crystal is racemic). A twist in the methine-C-C(carbonyl) bond [O-C-C-O torsion angle = 19.3 (7) ] leads to a dihedral angle of 22.2 (5) between the benzaldehyde and methine+methoxy residues. The chlorobenzene ring is folded to lie over the O atoms, with the dihedral angle between the benzene rings being 42.9 (2) . In the crystal, the carbonyl-O atom accepts two C-HÁ Á ÁO interactions with methyl-and methine-C-H atoms being the donors. The result is an helical supramolecular chain aligned along the c axis; chains pack with no directional interactions between them. An analysis of the Hirshfeld surface points to the important contributions of weak HÁ Á ÁH and CÁ Á ÁC contacts to the molecular packing.

Structural commentary
The molecular structure of (I) sees (4-chlorophenyl)sulfanyl, phenylethanone and methoxy groups linked at the chiral methine-C8 atom, Fig. 1. In the arbitrarily chosen asymmetric molecule, C8 has an R configuration, but crystal symmetry generates a racemic mixture. The base of the molecule is defined by the phenylethanone [r.m.s. deviation of the eight non-hydrogen atoms = 0.0134 Å ] and methoxy groups. These residues are not co-planar, with the dihedral angle between the two planes being 22.2 (5) owing to the twist about the C8-C9 bond as seen in the value of the O1-C8-C9-O2 torsion angle of 19.3 (7) . The 4-chlorophenyl group is orientated so that the ring lies over the oxygen atoms with the dihedral angle between the benzene rings being 42.9 (2) .

Supramolecular features
The molecular packing of (I) features C-HÁ Á ÁO interactions where the donors are methyl-C7 and methine-C8 H atoms, and the acceptor is the carbonyl-O2 atom, Table 1. These interactions combine to sustain a supramolecular chain along [001] with an helical topology as it is propagated by 2 1 symmetry, Fig. 2a. Chains assemble into the three-dimensional architecture without directional interactions between them, Fig. 2b.

Hirshfeld surface analysis
The Hirshfeld surface calculations for (I) were performed as per a recent study  and serve to provide additional information on the molecular packing, in   The molecular structure of (I), showing the atom-labelling scheme and displacement ellipsoids at the 35% probability level. Table 1 Hydrogen-bond geometry (Å , ). particular the weaker interactions between molecules. In addition to bright-red spots near the methyl-H7A and methine-H8 atoms, a pair near the carbonyl-O2 atom arise as a result of the C-HÁ Á ÁO interactions leading to the supramolecular chain discussed above, Table 1. The presence of diminutive and faint-red spots on the Hirshfeld surfaces illustrated in Fig. 3 indicate the influence of short interatomic contacts on the molecular packing in the crystal, Table 2. Thus, the CÁ Á ÁC and CÁ Á ÁH/HÁ Á ÁC contacts involving chlorobenzene-C6, carbonyl-C9 and methyl-H7C atoms are viewed as the pair of diminutive and faint-red spots near these atoms in Fig. 3, whereas similar features near the methyl-H7B, phenyl-C14 and -H14 atoms represent H7BÁ Á ÁH14 and CÁ Á ÁH/ HÁ Á ÁC contacts. Views of the Hirshfeld surfaces mapped over electrostatic potential are shown in Fig. 4 and also indicate the donors and acceptors of the C-HÁ Á ÁO interactions through the appearance of intense-blue and -red regions around the participating atoms. Fig. 5 illustrates the environment around a reference molecule within the d norm -mapped Hirshfeld surface and highlight the intermolecular C-HÁ Á ÁO interactions and short interatomic HÁ Á ÁH, CÁ Á ÁH/HÁ Á ÁC and CÁ Á ÁC contacts.

Figure 4
Two views of the Hirshfeld surfaces mapped over the electrostatic potential in the range À0.073 to + 0.056 au. The red and blue regions represent negative and positive electrostatic potentials, respectively.

Figure 5
A view of the Hirshfeld surface mapped over d norm in the range À0.073 to +1.389 au highlighting intermolecular C-HÁ Á ÁO, CÁ Á ÁC, HÁ Á ÁH and CÁ Á ÁH/HÁ Á ÁC contacts by black, red, yellow and sky-blue dashed lines, respectively.  Fig. 5 and Table 2. The small contribution from other remaining interatomic contacts summarized in Table 3 have a negligible influence upon the molecular packing.

Non-covalent interaction plots
Non-covalent interaction plots are a convenient means by which the nature of a specified intermolecular interaction may be assessed in terms of it being attractive or otherwise (Johnson et al., 2010;Contreras-García et al., 2011). If a specified interaction is attractive, the isosurface will be blue in appearance whereas a repulsive interaction will result in a red isosurface. On the other hand, a weakly attractive interaction will appear green. The isosurfaces for the interactions between the methyl-C7 and methine-C H atoms and the carbonyl-O2 atom are shown in Fig. 7a, clearly indicating their weakly attractive nature. Similarly, the interactions between the chlorobenzene-C6 and methyl-H7C atoms, Fig. 7b, and between the methyl-H7B and phenyl-H14 atoms, Fig. 7c, are weakly attractive.

Database survey
There are two closely related literature precedents for ( Non-covalent interaction plots for intermolecular interactions between (a) methyl-C7-and methine-C-H atoms, and the carbonyl-O2 atom, (b) chlorobenzene-C6 and methyl-H7C atoms and (c) methyl-H7B and phenyl-H14 atoms.
overlay diagram for (I)-(III) is shown in Fig. 8 from which it can be noted there is a high degree of concordance for (I) and (III). The molecule in (II) is coincident with (I) and (III) except for the relative disposition of the S-bound methoxybenzene ring. This difference arises as a result of a twist about the C8-S1 bond as seen in the C4-S1-C8-C9 torsion angles of 57.3 (5), 46.6 (3) and 57.9 (3) for (I)-(III), respectively. Despite this difference, the angles between the S-bound benzene rings and the phenyl rings in (I)-(III) are relatively constant at 42.9 (2), 40.11 (16) and 44.03 (16) , respectively.

Synthesis and crystallization
The 4 0 -chlorophenyl disulfide precursor was prepared as previously described (Ali & McDermott, 2002) through the oxidation of 4 0 -chlorothiophenol by bromine. A solution of 2-methoxy acetophenone (0.70 ml, 5.08 mmol, Sigma-Aldrich) in THF (15 ml), was added dropwise to a cooled (195 K) solution of diisopropylamine (0.78 ml, 5.59 mmol) and n-butyllithium (3.76 ml, 5.08 mmol) in THF (25 ml). After 30 min., a solution of 4 0 -chlorophenyl disulfide (1.61 g, 5.08 mmol) with hexamethylphosphoramide (HMPA) (0.90 ml, ca 5.08 mmol) dissolved in THF (15 ml) was added dropwise to the enolate solution (Zoretic & Soja, 1976). After stirring for 3 h, water (50 ml) was added at room temperature and extraction with diethyl ether was performed. The organic layer was then treated with a saturated solution of ammonium chloride until neutral pH and dried over anhydrous magnesium sulfate. A brown oil was obtained after evaporation of solvent. Purification through flash chromatography with n-hexane was used in order to remove the non-polar reactant (disulfide), then with dry acetone to give a mixture of both acetophenones (product and reactant). Crystallization was performed by vapour diffusion of n-hexane into a chloroform solution held at 283 K to give pure product (0.4 g, yield = 60%). Irregular colourless crystals for X-ray diffraction of (I) were obtained by the same pathway.

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 4. The carbon-bound H atoms were placed in calculated positions (C-H = 0.93-0.98 Å ) and were included in the refinement in the riding-model approximation, with U iso (H) set to 1.2-1.5U eq (C).

2-[(4-Chlorophenyl)sulfanyl]-2-methoxy-1-phenylethan-1-one
Crystal data 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.