c-3,t-3-Dimethyl-r-2,c-6-diphenylpiperidin-4-one

In the title compound, C19H21NO, the piperidine ring adopts a chair conformation. The two phenyl rings attached to the piperidine ring at 2 and 6 positions occupy equatorial orientations and the dihedral angle between them is 57.53 (11)°. In the crystal, the molecules are connected via weak intermolecular C—H⋯π interactions, leading to a zigzag chains.

In the title compound, C 19 H 21 NO, the piperidine ring adopts a chair conformation. The two phenyl rings attached to the piperidine ring at 2 and 6 positions occupy equatorial orientations and the dihedral angle between them is 57.53 (11) . In the crystal, the molecules are connected via weak intermolecular C-HÁ Á Á interactions, leading to a zigzag chains.

Comment
Various piperidine derivatives are present in numerous alkaloids (Badorrey et al., 1999). Piperidines have been found to exhibit blood cholesterol-lowering activities (Nalanishi et al., 1974). Trans-platinum piperidine derivatives deserve evaluation of their efficacy in tumor-bearing animals (Elena et al., 2002). In view of these importance, the crystal structure of the title compound has been carrried out.
The molecules are connected via intermolecular C-H···π interactions (Table 1) which lead to a zig-zag chain running along b -axis in addition to van der Waals forces (Fig. 2).

Experimental
The procedure reported by Noller and Baliah was followed for the preparation of this compound (Noller & Baliah, 1948).
Benzaldehyde (21ml), 3-methyl-2-butanone (10ml) and ammonium acetate (8gm) were dissolved in distilled ethanol (50ml) and heated over boiling water bath with shaking, until an yellow colour developed and changed into orange. The solution was left undisturbed for 14 hours. The solid thrown out was filtered, purified and recrystallized from ethanol.

Refinement
The H atom bonded to N was freely refined. H atoms bonded to C were positioned geometrically (C-H = 0.93 -0.98 Å) and allowed to ride on their parent atoms, with U iso (H) = 1.5U eq (C) for methyl H and 1.2U eq (C) for other H atoms. The components of the anisotropic displacement parameters of C18 and C19 in the direction of the bond between them were restrained to be equal within an effective standard deviation of 0.001. Fig. 1. The ORTEP plot of the molecule with 30% probability displacement ellipsoids.

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 > 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.