6-Hydroxy-7,8-dimethylchroman-2-one

The title compound, C11H12O3, is essentially planar, with an r.m.s. deviation of 0.179 Å from the mean plane through the 14 non-H atoms in the molecule. The benzene ring and the pyranone mean plane are inclined at 13.12 (6)° to one another and the pyranone ring adopts a flattened chair conformation. In the crystal, O—H⋯O hydrogen bonds and C—H⋯O contacts form R 1 2(6) rings and link molecules into chains along b. Additional C—H⋯O contacts generate inversion dimers, with R 2 2(8) ring motifs, and form sheets parallel to (-102) which are linked by C—H⋯π interactions.

The title compound, C 11 H 12 O 3 , is essentially planar, with an r.m.s. deviation of 0.179 Å from the mean plane through the 14 non-H atoms in the molecule. The benzene ring and the pyranone mean plane are inclined at 13.12 (6) to one another and the pyranone ring adopts a flattened chair conformation. In the crystal, O-HÁ Á ÁO hydrogen bonds and C-HÁ Á ÁO contacts form R 1 2 (6) rings and link molecules into chains along b. Additional C-HÁ Á ÁO contacts generate inversion dimers, with R 2 2 (8) ring motifs, and form sheets parallel to (102) which are linked by C-HÁ Á Á interactions.
Data collection: APEX2 (Bruker, 2011); cell refinement: APEX2 (Bruker, 2011) and SAINT (Bruker, 2011); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008) and TITAN2000 (Hunter & Simpson, 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008) and TITAN2000; Our current research is focused on the preparation of quinone/hydroquinone based monomers for utilization in redoxactive polymer gels. Synthesis of such systems is a multi-step process and often passes through a hydropyranone intermediate (Lecea et al., 2010;Cameron et al., 2011;Goswami et al., 2011). The title compound illustrates one such intermediate and was isolated during the synthesis of a trifluoromethyl substituted hydroquinone.
The title compound (I), Fig 1, is almost planar with an r.m.s. deviation of 0.179 Å from the best fit plane through the 14 non-hydrogen atoms in the molecule. The maximum deviation from this plane is 0.5437 (11) Å for C2. This is in keeping with the fact that the pyranone ring adopts a flattened chair conformation with the C2 atom displaced by 0.6004 (17) Å from the plane through C1/O2/C5/C4/C3 which, in turn, has an r.m.s. deviation of 0.076 Å. This is in contrast to the closely related 5,6-dimethyl-1,2,9,10-tetrahydropyrano[3,2-f]chromene-3,8-dione (Goswami et al., 2012), where both the C2 and O2 atoms of the pyranone rings were displaced significantly from the molecular plane in opposite directions. A search of the Cambridge Structural Database (Allen, 2002) revealed only two additional tetrahydropyrano derivatives , Cameron et al., 2011. However, removing the restraint on substitution at the 3 and 4 positions of the pyranone ring, reveals the structures of more than 190 chromanone derivatives. The bond distances (Allen et al., 1987) and angles in the molecule are normal and, despite the variation in the pyranone ring conformations, similar to those found in related structures (Goswami et al., , 2012Cameron et al., 2011).

Experimental
The title compound was prepared according to the literature (Lecea et al., 2010) by a Friedel-Crafts type reaction of 2,3dimethylhydroquinone with acrylic acid. X-ray quality crystals of (I) were grown from CDCl 3 .

Refinement
Crystals of this material were not of good quality and the results presented here represent the best of several data collections. All H-atoms bound to carbon were refined using a riding model with d(C-H) = 0.99 Å, U iso = 1.2U eq (C) for methylene and 0.98 Å, U iso = 1.5U eq (C) for CH 3 H atoms. The H8O hydrogen atom was located in a difference Fourier synthesis and its coordinates refined with U iso = 1.5U eq (O).

Figure 1
The structure of (I) with ellipsoids drawn at the 50% probability level.    Overall packing of (I) showing representative C-H···π contacts as dotted lines. The red spheres represent the centroids of the C4···C9 benzene rings and hydrogen bonds are drawn as dashed lines. Hydrogen site location: inferred from neighbouring sites H atoms treated by a mixture of independent and constrained refinement w = 1/[σ 2 (F o 2 ) + (0.0874P) 2 + 0.1584P] where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.60 e Å −3 Δρ min = −0.28 e Å −3 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.