N′-[(E)-4-Chlorobenzylidene]-2-(4-isobutylphenyl)propanohydrazide

The asymmetric unit of title compound, C20H23ClN2O, consists of two crystallographically independent molecules (A and B) in which the orientations of the 4-isobutylphenyl units are different. The isobutyl group of molecule B is disordered over two positions with occupancies of 0.850 (5) and 0.150 (5). The dihedral angle between the two benzene rings is 88.70 (9)° in molecule A and 89.38 (9)° in molecule B. The independent molecules are linked together into chains along [100] by N—H⋯O and C—H⋯O hydrogen bonds, and by C—H⋯π interactions. In the chain, N—H⋯O and C—H⋯O hydrogen bonds generate R 2 1(6) ring motifs. In addition, C—H⋯N hydrogen bonds are observed. The presence of pseudosymmetry in the structure suggests the higher symmetry space group Pbca but attempts to refine the structure in this space group resulted in high R (0.119) and wR (0.296) values.

The asymmetric unit of title compound, C 20 H 23 ClN 2 O, consists of two crystallographically independent molecules (A and B) in which the orientations of the 4-isobutylphenyl units are different. The isobutyl group of molecule B is disordered over two positions with occupancies of 0.850 (5) and 0.150 (5). The dihedral angle between the two benzene rings is 88.70 (9) in molecule A and 89.38 (9) in molecule B. The independent molecules are linked together into chains along [100] by N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds, and by C-HÁ Á Á interactions. In the chain, N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds generate R 2 1 (6) ring motifs. In addition, C-HÁ Á ÁN hydrogen bonds are observed. The presence of pseudosymmetry in the structure suggests the higher symmetry space group Pbca but attempts to refine the structure in this space group resulted in high R (0.119) and wR (0.296) values.  (2003). For bondlength data, see: Allen et al. (1987). For hydrogen-bond motifs, see: Bernstein et al. (1995). For the crystal structure of the bromo analogue, see: Fun et al. (2009). For the stability of the temperature controller used for the data collection, see: Cosier & Glazer (1986).

N'-[(E)-4-Chlorobenzylidene]-2-(4-isobutylphenyl)propanohydrazide
H.-K. Fun, C. S. Yeap, K. V. Sujith and B. Kalluraya Comment Non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen are widely used in the treatment of pain and inflammation (Kawail et al., 2005;Klasser & Epstein, 2005). Aryl hydrazones are important building blocks for the synthesis of a variety of heterocyclic compounds such as pyrazolines and pyrazoles (Sridhar & Perumal, 2003). Aryl hydrazones have been most conveniently synthesized by the reaction of aryl hydrazines with carbonyl compounds. Hydrazones possessing an azometine -NHN=CH-proton constitute an important class of compounds for new drug development. Hydrazones have been demonstrated to possess antimicrobial, anticonvulsant, analgesic, antiinflammatory, antiplatelet, antitubercular, anticancer and antitumoral activities (Bedia et al., 2006;Rollas et al., 2002;Terzioglu & Gürsoy, 2003). These observations have been the guide for the development of new hydrazones that possess varied biological activities. Prompted by these observations, the title compoud was synthesized and its crystal structure is reported here.
The asymmetric unit of title compound (Fig. 1), consists of two crystallographically independent molecules, A and B, in which the orientations of the 4-isobutylphenyl units are different (Table 1). Bond lengths (Allen et al., 1987) and angles are within normal ranges and are comparable with those in the bromo analogue (Fun et al., 2009). The dihedral angle between the two benzene rings is 88.70 (9)° in molecule A and 89.38 (9)° in molecule B. The molecule A is linked to the molecule B by intermolecular C7A-H7AA···O1B and N2A-H1NA···O1B hydrogen bonds, generating an R 2 1 (6) ring motif (Bernstein et al., 1995) and by an C-H···π interaction.
In the crystal structure, the independent molecules are linked together into chains along the [100] (Fig. 2) by N-H···O and C-H···O hydrogen bonds, and C-H···π interactions (Table 2). In addition, C-H···N hydrogen bonds are observed.

Experimental
A mixture of 2-[4-(2-methylpropyl)phenyl]propanehydrazide (0.01 mol) and 4-chlorobenzaldehyde (0.01 mol) in ethanol (30 ml) along with 3 drops of concentrated sulphuric acid was refluxed for 1 h. Excess ethanol was removed from the reaction mixture under reduced pressure. The solid product obtained was filtered, washed with ethanol and dried. Single crystals suitable for X-ray analysis were obtained by slow evaporation of an ethanol solution (yield 87%; m.p.430-433 K).

Refinement
The isopropyl group of molecule B is disordered over two positions with occupancies of 0.850 (5) and 0.150 (5). H atoms were positioned geometrically and refined using a riding model, with N-H = 0.86 Å, C-H = 0.93-0.98 Å and U iso (H) = 1.2-1.5 U eq (N, C). A rotating-group model was applied for the methyl groups. The presence of pseudo-symmetry in the structure suggests a higher symmetry space group Pbca. But attempts to refine the structure in the space group Pbca resulted in a more disordered model with high R (0.119) and wR (0.296) values. Fig. 1. The asymmetric unit of the title compound, with atom labels and 50% probability displacement ellipsoids for non-H atoms. Hydrogen bonds are shown as dashed lines. Both disorder components are shown.   Glazer, 1986) operating at 100.0 (1)K.

N'-[(E)-4-Chlorobenzylidene]-2-(4-isobutylphenyl)propanohydrazide
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 > 2sigma(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.