3-(3,4-Dichlorobenzylidene)chroman-4-one

The distinctive feature of the structure of the title compound, C16H10Cl2O2, is the formation of a zigzag chain along [100] via Cl⋯Cl interactions [3.591 (1) and 3.631 (1) Å]. The chromanone moiety is fused with the benzene ring and adopts a half-chair conformation. The dihedral angle between the benzene ring of the chromanone moiety and the dichlorobenzene plane is 56.14 (8)°.

The distinctive feature of the structure of the title compound, C 16 H 10 Cl 2 O 2 , is the formation of a zigzag chain along [100] via ClÁ Á ÁCl interactions [3.591 (1) and 3.631 (1) Å ]. The chromanone moiety is fused with the benzene ring and adopts a halfchair conformation. The dihedral angle between the benzene ring of the chromanone moiety and the dichlorobenzene plane is 56.14 (8) .
A view of the the title compound is shown in Fig. 1. The chromanone moiety is fused with the benzene ring and adopts a half chair conformation. The dihedral angle between the benzene ring of the chromanone moiety and the dichlorobenzene plane is 56.14 (8)°. The inversion-related molecules are linked into zigzag chains via Cl···Cl interactions between Cl2 at (x, y, z) and Cl2 at (1 -x, 1 -y, 1 -z) and Cl2 at (-x, 1 -y, 1 -z) with distances of 3.591 (1) Å and 3.631 (1) Å respectively. Molecules related by translation along the a axis stack via double π···π interactions of the aromatic rings, with a centroid distance equal to the length of a axis. This feature is illustrated in Fig. 2.

Experimental
A mixture of chroman-4-one (1 g, 6.749 mmol), 3,4-dichlorobenzaldehyde (1.417 g, 8.099 mmol) and 10-15 drops of piperidine was heated at 80°C for 18 hrs. The reaction mixture was monitored for completion by thin layer chromatography. Upon completion, the reaction mixture was cooled, diluted with water and neutralized using 10% HCl.
The reaction mixture was extracted with ethyl acetate (3 × 30 ml). The ethyl acetate layers were combined, washed with brine (20 ml), water (2 × 10 ml) and dried over anhydrous magnesium sulfate. The solvent was reduced and the compound purified by column chromatography using silica gel (Merck 9385, 40-63 µm particle size) with a mobile phase of 2% ethyl acetate in hexane to yield the title compound with a m.p. of 165-167 °C.

Figure 1
Molecular structure of the title compound, showing the atom labelling scheme and with displacement ellipsoids drawn at the 50% probability level.

Figure 2
Partial packing diagram showing the Cl···Cl interactions and π···π stacking as dashed lines. H atoms have been omitted.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq