Crystal structure of 4-methyl-7-propoxy-2H-chromen-2-one

The asymmetric unit of the title compound contains two independent molecules that are interconnected through an offset π–π interaction. The fused benzene and pyran-2-one rings in each molecule are essentially coplanar. Similarly, the coumarin ring system and the 7-propoxy substituent are close to being coplanar.

The asymmetric unit of the title compound, C 13 H 14 O 3 , contains two independent molecules, A and B, that are interconnected through an offsetinteraction [inter-centroid separation = 3.6087 (4) Å ]. The fused benzene and pyran-2-one rings in each molecule are essentially coplanar, having dihedral angles of 1.22 (12) and 1.57 (12) for molecules A and B, respectively. Similarly, the coumarin ring system and the 7-propoxy substituent are close to being coplanar [C-C-O-C torsion angles = 2.9 (2) and 1.4 (2) for molecules A and B, respectively]. In the crystal, the molecules are connected by C-HÁ Á ÁO hydrogen bonds, forming supramolecular tapes along [100] that are linked into a three-dimensional network by C-HÁ Á Á interactions, as well as by the aforementionedinteractions.

Chemical context
Coumarin (2H-1-benzopyran-2-one) is a plant-derived natural product known for its pharmacological properties such as antiinflammatory, anticoagulant, antibacterial, antifungal, antiviral, anticancer, antihypertensive, antitubercular, anticonvulsant, anti-adipogenic, antihyperglycemic, anti-oxidant and neuroprotective properties. Dietary exposure to benzopyrones is significant as these compounds are found in vegetables, fruits, seeds, nuts, coffee, tea and wine (Venugopala et al., 2013). In order to assist our knowledge about the stereoelectronic requirements from these kinds of molecules to show anti-asthmatic or tracheal relaxant actions, we have synthesized (Sá nchez-Recillas et al., 2014) and determined the crystal structure of the title compound, (I). A related structure, 3acetylcoumarin, has been reported on by Munshi et al. (2004).

Structural commentary
The asymmetric unit of (I) contains two independent molecules (A and B). Bond lengths between equivalent non-H atoms of each molecule are similar, with differences less than 3 s.u.

Synthesis and crystallization
The title compound was prepared by SN2 reaction between 7hydroxy-4-methyl-2H-chromen-2-one and n-propyl bromide. 7-Hydroxy-4-methyl-2H-chromen-2-one (0.4 g, 2.27 mmol) and potassium carbonate (1.28 g, 9.30 mmol, 4.1 equiv) were dissolved in acetone (2.0 ml) and kept at room temperature. After 20 minutes, n-propylbromide (0.641 ml, 7.03 mmol) was added drop wise and the reaction mixture was heated to reflux (313 K) and monitored by TLC. After completion of the reaction (six days), the reaction mixture was filtered and the solid residue was washed off with cold water (10 ml). The total mother liquors were concentrated under reduced pressure and then poured into water and extracted with ethyl acetate (3 Â The molecular structure of (I), showing the atom-labelling scheme and the offsetinteraction. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radius. The dashed line indicates the interaction between the benzene ring centroids Cg1 (C4-C9) and Cg2 (C17-C22). Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
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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.