N-(2,6-Diisopropylphenyl)thioamide

In the crystal structure of the title compound, C13H19NS {systematic name: N-[2,6-bis(propan-2-yl)phenyl]carbothioamide}, molecules assemble via N—H⋯S=C hydrogen bonds into helical chains along the b axis. The thioamide moiety, with a syn disposition of the N- and C-bound H atoms, is twisted out of the plane of the benzene ring to which it is connected, forming a dihedral angle angle of 77.60 (14)°.


Comment
The synthesis of arylthioamides related to the title compound has been described (Fernandes & Reid, 2003) as have the structures of related thioamides (Chitanda et al., 2008;Michta et al., 2008;Omondi et al., 2009a;Jarchow & Schmalle, 1977) and N-2,6-disubstituted-arylformamides (Omondi et al., 2009b;Omondi et al., 2009c;Omondi et al., 2008). In a previous study of 2,6-disubstituted N-arylformamides (Omondi et al., 2005), we analyzed the effect of chloro-methyl exchange and the role of weak interactions on the structural and thermal properties of the compounds studied. Phase transitions were observed when the substituents were either both chloride (2,6-dichloro-phenylformamide) or one chloride and one methyl group (2-chloro-6-methyl-phenylformamide); see also Gowda et al. (2000). In a subsequent study we analysed the crystal structures of several N-arylthioamides (Omondi et al., 2009a) with a view to understanding the influence of hydrogen bonds and other weak intermolecular interactions on the conformation and the overall crystal packing of these compounds. The structure of 2,6-diisopropyl-N-phenylformamide, 2, was reported recently (Chitanda et al., 2008). In this paper we report on the crystal structure of the analogous 2,6-diisopropyl-N-phenylthioamide (1, Fig. 1).
The angle between the mean plane through the phenyl ring and the thioamide moiety in 1 is 77.60 (14)°, while in 2 the corresponding angle between the formamide and the phenyl plane is ca 79°. The overlay diagram between structures of 1 and 2 is shown in Fig. 2. In 1 chains of molecules are linked via N-H···S═C hydrogen bonds. Molecules along these chains are related by screw (2 1 ) symmetry as shown by the packing of the molecules in the unit cell (Fig. 3).

Experimental
The title compound was synthesized using a method similar to one described previously (Omondi et al., 2009a). A mixture of the parent formamide and P 2 S 5 was refluxed in a mixture of THF and benzene for about 60 min (monitoring the reaction progress was by TLC plates). The solvent was then removed in vacuo and the product extracted from the remaining solid using benzene. The pale-yellow solution was passed through a column (silica gel) using a 1:1 mixture of hexane and ethyl acetate as the carrier solvent. The product was crystallized directly from the carrier solution. Colourless, block-like crystals were obtained.

Refinement
The N-bound H atom on the amide was placed according to the observed electron density and allowed to refine freely.
The remaining H atoms were positioned geometrically and allowed to ride on their respective parent atoms, with C-H bond lengths of 0.93-0.98 Å and with U iso (H) = 1.2-1.5U eq (C). Isopropyl atoms C8-C13 were reported by PLATON to have slightly distorted anisotropic displacement parameters (ADP). As a consequence, DELU and SIMU were used in the final refinement to restrain their ADPs to more reasonable values.

Figure 1
The molecular structure of the title compound. Displacement ellipsoids are shown at the 30% probability level.  An overlay diagram between structures of the title compound and 2,6-diisopropyl-N-phenylformamide (2).

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 R-factors(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.