r-2,c-6-Bis(2-methoxyphenyl)-t-3,t-5-dimethylpiperidin-4-one acetic acid solvate

In the title compound, C21H25NO3·C2H4O2, the piperidone ring adopts a chair conformation. The two methoxy groups are nearly coplanar with the aromatic rings to which they are attached. The dihedral angle between the two aromatic rings is 60.9 (2)°. There are two short intramolecular N—H⋯O contacts. The crystal packing is stabilized by intermolecular O—H⋯N and C—H⋯O interactions.

In the title compound, C 21 H 25 NO 3 ÁC 2 H 4 O 2 , the piperidone ring adopts a chair conformation. The two methoxy groups are nearly coplanar with the aromatic rings to which they are attached. The dihedral angle between the two aromatic rings is 60.9 (2) . There are two short intramolecular N-HÁ Á ÁO contacts. The crystal packing is stabilized by intermolecular O-HÁ Á ÁN and C-HÁ Á ÁO interactions.

Comment
In continuation of our work on establishing the crystal structure and conformation of 2,6-diaryl piperidine-4-ones and their derivatives (Aridoss et al., 2008, 2009and Gayathri et al., 2008, we are reporting here the crystal structure of the title compound wherein the piperidone ring adopts chair conformation irrespective of the substituents' on both sides of carbonyl and secondary nitrogen in the ring. In the present structure, the piperidone ring adopts a chair conformation with atoms N1 and C3 deviating by -0.584 (2) and 0.628 (6) Å, respectively,from the least-sqaures plane defined by the remaining atoms (C1/C2/C4/C5) in the ring. When compared with the reported structures of piperidone derivatives (Gayathri et al., 2008), it is clear that the conformation of the piperidone ring is highly influenced by the substitutions at various positions. The molecule is stabilized by N-H···O intramolecular interaction wherein, N1 atom act as a donor to O2 and O3, generating two S(6) motifs. The crystal packing is stabilized by N-H···O, O-H···N and C-H···O intra and intermolecular interactions. The sum of the bond angles around the atom N1(336.6 (3)°) of the piperidone ring in the molecule is in accordance with sp 3 hybridization.

Experimental
The title compound was prepared by the condensation of 3-pentanone, 2-methoxybenzaldehyde and ammonium acetate in 1:2:1 molar ratio in ethanol as reported by Noller and Baliah (1948) with slight modification. Diffraction quality white crystal was obtained by recrystalization of the crude sample from ethanol.

Refinement
H atoms bonded to C and O were positioned geometrically (C-H=0.93-0.98Å, O-H =0.82Å) and allowed to ride on their parent atoms, with 1.5U eq (C methyl ,O) or 1.2 U eq (C). The H atom bonded to N was isotropically refined.

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.