1-Formyl-t-3,t-5-dimethyl-r-2,c-6-diphenylpiperidin-4-one

In the title compound, C20H21NO2, the piperidine ring adopts a distorted boat conformation. The dihedral angle between the two phenyl rings is 61.33 (18)°. In the crystal, intermolecular C—H⋯O interactions link the molecules into zigzag C(5) chains running parallel to [100].

In the title compound, C 20 H 21 NO 2 , the piperidine ring adopts a distorted boat conformation. The dihedral angle between the two phenyl rings is 61.33 (18) . In the crystal, intermolecular C-HÁ Á ÁO interactions link the molecules into zigzag C(5) chains running parallel to [100].
Atom C6 at (x, y, z) acts as a hydrogen-bond donor to atom O2 of the molecule at (x-1/2, y, 1/2-z) forming a zigzag C(5) chain (Bernstein et al., 1995) running along the a axis, as shown in Fig. 2.
The reaction mixture was stirred at room temperature for 5 h. The organic layer was separated, dried over anhydrous Na 2 SO 4 and concentrated. The resulting mass was purified and crystallized from benzene-petroleum ether (333-335 K) in the ratio 1:1 (Jeyaraman et al., 1999).

Refinement
Atom H7 was located in a difference map and its positional parameters were refined. The remaining H atoms were positioned geometrically (C-H =0.93-0.98 Å, ) and allowed to ride on their parent atoms, with 1.5U eq (C) for methyl and 1.2 U eq (C) for other H atoms. The U ij parameters of atoms O1, C7, C10 and C11 were restrained to an approximate isotropic behaviour.

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.