2-[(E)-4-Methoxybenzylidene]-1,2,3,4-tetrahydronaphthalen-1-one

Two independent molecules (A and B) comprise the asymmetric unit of the title compound, C18H16O2. Molecule B is virtually superimposable upon A. Minor differences are noted in the dihedral angles between the terminal benzene rings of 56.03 (10) and 54.62 (10)°, and in the orientations of methoxy groups with respect to the benzene rings to which they are attached [C—O—C—C torsion angles = 169.11 (19) and −172.37 (18)°]. The cyclohexene ring of each fused ring system has a screw-boat conformation. In the crystal, C—H⋯π interactions assemble molecules into a supramolecular array in the ab plane.

Two independent molecules (A and B) comprise the asymmetric unit of the title compound, C 18 H 16 O 2 . Molecule B is virtually superimposable upon A. Minor differences are noted in the dihedral angles between the terminal benzene rings of 56.03 (10) and 54.62 (10) , and in the orientations of methoxy groups with respect to the benzene rings to which they are attached [C-O-C-C torsion angles = 169.11 (19) and À172.37 (18) ]. The cyclohexene ring of each fused ring system has a screw-boat conformation. In the crystal, C-HÁ Á Á interactions assemble molecules into a supramolecular array in the ab plane.

Related literature
For the activity of related species developed for the treatment of Chagas disease, see: Vera-DiVaio et al. (2009). For the structure of the 2-methoxy derivative, see: Dimmock et al. (2002). For conformational analysis, see: Cremer & Pople (1975 Table 1 Hydrogen-bond geometry (Å , ).
Two independent molecules comprise the asymmetric unit of (I), Fig. 1. The inverted structure of the O3-containing molecule is virtually super-imposable upon the O1-containing molecule, Fig. 2. The cyclohexene ring of each fused ring system has a screw boat conformation (Cremer & Pople, 1975). A difference between the molecules is seen in the dihedral angles between the terminal benzene rings of 56.03 (10) and 54.62 (10)°, respectively. The methoxy groups are co-planar with the benzene rings to which they are attached as seen in the C18-O2-C15-C14 and C36-O4-C33-C32 torsion angles of 169.11 (19) and -172.37 (18)°, respectively. The conformation about each ethylene bond is E. The overall molecular conformation observed for the independent molecules of (I) resembles that seen in the 2-methoxy derivative (Dimmock et al., 2002).
The presence of C-H···π interactions link molecules into a supramolecular array in the ab plane in the crystal structure of (I), Fig. 3 and Table 1. Layers stack along the c axis with no specific interactions between them (Fig. 4).

Experimental
A solution of the 4-methoxybenzaldehyde (1.3 g, 0.01 M) in ethanol (20 ml) was added to a stirred solution of 1-tetralone (1.46 g,0.01 M) in ethanolic KOH (20 ml, 20%), and stirring was maintained at room temperature for 6 h. The reaction mixture was then poured onto water (200 ml) and set aside overnight. The precipitated solid product was collected by filtration, washed with water, dried and recrystallized from ethanol. Yield: 92%.

Refinement
H-atoms were placed in calculated positions [C-H = 0.95 Å, U iso (H) = 1.2U eq (C)] and were included in the refinement in the riding model approximation. One reflection, i.e. (-3 6 3), was omitted from the final refinement owing to poor agreement.

Figure 2
Superimposition of the two independent molecules in (I). The fused ring systems have been superimposed. The O1 and inverted O3-containing molecules are shown as red and blue images, respectively.

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.