2-(Diphenylmethylidene)-2,3-dihydro-1H-inden-1-one

In the title molecule, C22H16O, the indanone ring system is approximately planar with a dihedral angle between the fused rings of 5.13 (14)°. Two benzene rings are linked together at one side of a double bond, sitting on either side of the indanone ring system and making dihedral angles of 70.30 (12) and 44.74 (13)° with it. In the crystal, hydrogen bonding is not present, but weak C—H⋯π or π–π interactions occur and molecules form a sheet-like structure in the bc plane.

In the title molecule, C 22 H 16 O, the indanone ring system is approximately planar with a dihedral angle between the fused rings of 5.13 (14) . Two benzene rings are linked together at one side of a double bond, sitting on either side of the indanone ring system and making dihedral angles of 70.30 (12) and 44.74 (13) with it. In the crystal, hydrogen bonding is not present, but weak C-HÁ Á Á orinteractions occur and molecules form a sheet-like structure in the bc plane.
The asymmetric unit of the title molecule (I) is shown in Figure 1. It crystallizes in the non-chiral, monoclinic space group P2 1 /c. The two benzene rings, C8-C13 and C1-C6 in the molecule lie above and below the C16-C21 plane, with the dihedral angles 70.30 (12)° and 44.74 (13)°, respectively. The torsion angles of these two benzene groups are can be considered as a planar triangle: C14-C7-C8 = 119.0 (2)°, C14-C7-C6 = 126.2 (3)° and C6-C7-C8 = 114.6 (2)°. The packing diagrams of the molecular structure are presented in Figure 2. Weak intermolecular C-H···π and π-π interactions are observed in Figure 2a, which seems to be very effective in the stabilization of the crystal structure. Figure 2b shows that the molecules are separated by forming a sheet-like structure in the bc-plane when viewed along the crystallographic b-axis. It is suggested that weak Van der Vaals force or electrostatic interaction could be contributed to the linkage of the sheets.

Experimental
To a stirred solution of 2-((2-hydroxyethoxy)diphenylmethyl)-2,3-dihydroinden-1-one (2.23 mmol) in methanol/DCM (12 ml, v:v, 3:1) was added trifluoromethanesulfonic acid (0.2 ml). The reaction was stirred at reflux for one hour, after which time the reaction was quenched by the addition of 2M NaOH aq. solution (20 ml) and the product was extracted with DCM (3 x 25 ml). The combined organic extracts were dried over magnesium sulfate, filtered and concentrated in vacuo, and the residue was purified by flash column chromatography on silica gel 230-400mesh (eluent: hexane: ethyl acetate, 10:1). All homogenous fractions were collected and the solvent removed in vacuo to afford titled crossed aldol condensed compound (94%) as yellow solid. Crystals suitable for X-ray diffraction were obtained after 7 days of slow evaporation of an ethyl acetate solution.

Refinement
All H atoms were placed in geometrically idealized positions and treated using the riding model, with C-H = 0.93-0.97 Å for H atoms. U iso (H) values were set at 1.2-1.5 times U eq (C) for the H atoms in the molecule.

Figure 1
The molecule structure of the titled compound with the atom numbering scheme. Displacement ellipsoids are shown at the 50% probability level. H atoms are presented as small spheres of arbitrary radius.    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.