9-(2-Chlorobenzylidene)anthracen-10(9H)-one

In the title compound, C21H13ClO, the central anthracene system is distorted towards a boat conformation and the outer rings are not coplanar with the central ring [dihedral angles = 7.79 (1) and 11.90 (1)°]. The crystal structure features inversion dimers with graph-set motif R 2 2(18) formed by C—H⋯O interactions.

In the title compound, C 21 H 13 ClO, the central anthracene system is distorted towards a boat conformation and the outer rings are not coplanar with the central ring [dihedral angles = 7.79 (1) and 11.90 (1) ]. The crystal structure features inversion dimers with graph-set motif R 2 2 (18) formed by C-HÁ Á ÁO interactions.

Suresh Comment
The compound anthracene has been known for a long time and its properties have been extensively studied. The regio and sterio-selectivity of substituted anthracenes in Diels-Alder reactions have been investigated and reported (Alston et al., (1979); Meek et al., (1960); Kaplan & Conroy, 1963;Verma & Singh, 1977;Singh & Ningombom, 2010). In view of this we have synthesized the title compound to study its crystal structure.
In the title compound (Fig 1),C 21 H 13 ClO, the benzene rings A and C in the anthracene moiety are almost individually planar with r.m.s deviation of 0.0071, and 0.0107 Å, respectively.The central anthracene ring B is distorted towards a boat conformation as evidenced by the puckering parameters q 2 = 0.2074 (17) Å, θ = 76.8 (5)°, φ =5.9 (5)° (Cremer & Pople, 1975). The aromatic ring B is not coplanar with the aromatic rings A and C, as evidenced by the dihedral angles of in the anthracene fragment are as expected for this type of molecule. In the crystal structure the C17-H17···O1 hydrogen bond connects two centrosymmetrically related molecules into dimers (Fig. 2) and generates a graph set motif of R 2 2 (18) (Bernstein et al., 1995). These centrosymmetric dimers are packed by weak Van der Waals interactions.

Experimental
A mixture of anthrone (500 mg, 2.57) and 2-chlorobenzaldehyde (362 mg, 2.57 mmol) were dissolved in ethanol (10 ml) at room temperature. Then, the reaction mixture was saturated with gaseous hydrogen chloride for 1 h. The reaction mixture became dark and was thereafter heated to reflux for 1 h. After completion of the reaction as evidenced by TLC, the reaction mixture was cooled to room temperature. The solid product was filtered and dried at room temperature and recrystallized through ethyl acetate by slow evaporation technique. Melting point: 125°C,Yield: 85%

Refinement
H atoms were placed at calculated positions and allowed to ride on their carrier atoms with C-H = 0.93 Å. U iso = 1.2U eq (C) for CH 2 and CH groups and U iso = 1.5U eq (C) for CH 3 group.

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.