2-Hydroxy-2-trifluoromethyl-3,4-dihydro-2H-1-benzopyran-4-one

The heterocyclic ring in the title compound, C10H7F3O3, has a half-boat conformation with the hydroxy-bearing C atom lying 0.595 (3) Å out of the plane of the five remaining atoms (r.m.s. deviation = 0.022 Å) in the direction of the hydroxy O atom. Linear supramolecular chains along the a axis, sustained by O—H⋯O hydrogen bonds between the hydroxy H and ketone O atoms, feature in the crystal packing. These chains are connected into a three-dimensional architecture by C—H⋯O and C—H⋯F contacts.

Data collection: CrysAlis PRO (Agilent, 2012); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010  In (I), Fig. 1, the heterocyclic ring has a half-boat conformation with the hydroxy bearing C9 atom lying 0.595 (3) Å out of the plane of the five remaining atoms [r.m.s. deviation = 0.022 Å] in the direction of the hydroxy O3 atom. A similar conformation was found in a literature precedent with phenyl rather than CF 3 and with OH and two OMe substituents on the benzene ring (Wang et al., 1999).
In the crystal, linear supramolecular chains sustained by O-H···O hydrogen bonds between the hydroxy H and ketone-O atoms (Table 1), are formed along the a axis (Fig. 2). These are connected into a three-dimensional architecture by C-H···O and C-H···F contacts ( Fig. 3 and Table 1).

Refinement
Carbon-bound H-atoms were placed in calculated positions [C-H = 0.95-0.99 Å, U iso (H) = 1.2U eq (C)] and were included in the refinement in the riding model approximation. The oxygen-bound H-atom was located in a difference Fourier map and was refined freely.

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 F1