7-Fluoro-4-oxochromene-3-carbaldehyde

In the title compound, C10H5FO3, the chromenone ring is essentially planar, with a maximum deviation of 0.039 (1) Å. The dihedral angle between the fluoro-subsituted benzene ring and the pyran ring is 1.92 (4)°. In the crystal, molecules are connected via weak intermolecular C—H⋯O hydrogen bonds, forming supramolecular ribbons along the b axis. These ribbons are stacked down the a axis.

In the title compound, C 10 H 5 FO 3 , the chromenone ring is essentially planar, with a maximum deviation of 0.039 (1) Å . The dihedral angle between the fluoro-subsituted benzene ring and the pyran ring is 1.92 (4) . In the crystal, molecules are connected via weak intermolecular C-HÁ Á ÁO hydrogen bonds, forming supramolecular ribbons along the b axis. These ribbons are stacked down the a axis.

Experimental
To a well stirred solution of 4-fluoro-2-hydroxyacetophenone (6.5 mmol, 1.0 g) in DMF (4 ml), POCl 3 (26.1 mmol, 2.4 ml) was added dropwise with stirring in ice bath. After 15 minutes, the ice bath was removed and the reaction mixture was continued to be stirred at room temperature for overnight. The resultant reaction mixture was then decomposed by crushed ice and the final product was collected by filtration, washed with ethanol-water and recrystallized from acetone to afford the title compound in 75% yield.

Refinement
All the H atoms were positioned geometrically [ C-H = 0.93 Å ] and were refined using a riding model, with U iso (H) = 1.2 U eq (C). The highest peak in the final difference map was found at a distance of 0.68 Å from C3 and the deepest hole was 0.79 Å from C2.    (Cosier & Glazer, 1986) operating at 100.0 (1) K.
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(F 2 ) is used only for calculating Rfactors(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.