5-(Diphenylmethylidene)pyrrolidin-2-one

In the title compound, C17H15NO, the dihedral angle between the phenyl rings is 80.1 (2)°. In the crystal, molecules are linked by pairs of N—H⋯O hydrogen bonds, forming inversion dimers.

In the title compound, C 17 H 15 NO, the dihedral angle between the phenyl rings is 80.1 (2) . In the crystal, molecules are linked by pairs of N-HÁ Á ÁO hydrogen bonds, forming inversion dimers.
We gratefully acknowledge financial support in part from the National Science Council, Taiwan (NSC 99-2119-M-241-001-MY2). Helpful comments from the reviewers were also greatly appreciated. The title compound (I) is the side product obtained from the attempted synthesis of 5-(diphenylmethyl)pyrrolidin-2-one (Fujihara et al., 1999;Enders et al., 2008). We found that adding excess calcium hydride to the reaction mixture could improve the yield of (I). Herein we report the synthesis and crystal structure of the (I). The molecular structure of (I) is shown in Fig. 1
The organic layer was dried over MgSO 4 and concentrated in vacuo. The residue was separated by chromatography over silica gel and eluted with hexane/ethyl acetate (6/4) to afford 100 mg of the title compound (I) in 73% yield. Single crystals suitable for X-ray measurements were obtained by recrystallization from a dichloromethane/hexane solution of the title compound at room temperature.

Refinement
All H atoms were placed in geometrically idealized positions and treated as riding on their parent atoms, with C-H = 0.93 or 0.97 Å, N-H = 0.86 Å and U iso (H) = 1.2U eq (C, N).  The molecular structure of (I), with ellipsoids for non-H atoms shown at the 50% probability level.

Figure 2
A hydrogen-bonded (dashed lines) dimer of (I). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.31 e Å −3 Δρ min = −0.26 e Å −3 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.