Crystal structure of (E)-2-(4-chlorobenzylidene)-3,4-dihydronaphthalen-1(2H)-one: a second monoclinic polymorph

The title compound, C17H13ClO, is the second monoclinic polymorph to crystallize in the space group P21/c. The first polymorph crystallized with two independent molecules in the asymmetric unit [Bolognesi et al. (1975 ▸). Acta Cryst. A31, S119; Z′ = 2; no atomic coordinates available], whereas the title compound has Z′ = 1. In the title polymorph, the dihedral angle between the plane of the benzene ring of the tetralone moiety and that of the 4-chlorobenzyl ring is 52.21 (11)°. The cyclohex-2-en-1-one ring of the tetralone moiety has a screw-boat conformation. In the crystal, molecules are liked by pairs of C—H⋯π interactions forming inversion dimers. There are no other significant intermolecular interactions present.

In the crystal, molecules are liked by pairs of C-H···π interactions forming inversion dimers (Table 1). There are no other significant intermolecular interactions present.

S2. Synthesis and crystallization
The synthesis of the title compound was carried out following a published procedure (Kerbal et al., 1988), viz. by a condensation of equimolar amounts of 4-chlorobenzaldehyde and α-tetralone using sodium hydroxide in methanol (yield; 87%; m.p.: 426-428 K). The synthesized compound was crystallized in tetrahydrofuran under slow evaporation yielding light-orange prismatic crystals.

S3. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The H-atoms were positioned geometrically (C-H = 0.93-0.97 Å) and refined as riding with U iso (H) = 1.2U eq (C).

Figure 1
View of the molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

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.