1-(5,7-Dihydroxy-2,2-dimethylchroman-6-yl)ethanone

In the title molecule, C13H16O4, the pyran ring is in a half-chair conformation. There is an intramolecular hydrogen bond involving the ketone O atom and an H atom of a phenol group which forms an S(6) ring. The ketone O atom is also involved in an intermolecular hydrogen bond with a different phenolic H atom of a symmetry-related molecule, forming C(6) chains along the c-axis direction.

In the title molecule, C 13 H 16 O 4 , the pyran ring is in a half-chair conformation. There is an intramolecular hydrogen bond involving the ketone O atom and an H atom of a phenol group which forms an S(6) ring. The ketone O atom is also involved in an intermolecular hydrogen bond with a different phenolic H atom of a symmetry-related molecule, forming C(6) chains along the c-axis direction.    (Kraus et al., 2011). It has also been obtained as a side product in the preparation of prenylated flavonoids with antitumour activity (Basabe et al., 2010). The molecular structure of the title compound is shown in Fig. 1. The pyran ring is in a half-chair conformation. There are two types of hydrogen bonds, one intramolecular and one intermolecular. The intramolecular O3-H103···O4 hydrogen bond forms an S(6) ring motif (Bernstein et al., 1995). This hydrogen bond motif is common to molecules which contain derivatized (2-hydroxyphenyl)ethanone structures (Chakkaravarthi et al., 2007). In addition to the intramolecular hydrogen bonding, there is an intermolecular hydrogen bond between the phenolic group and the ketone O atom of an adjacent molecule. This O2-H102···O4 i (see Table 1 for symmetry code) hydrogen bond links the molecules to form infinite one-dimensional C(6) chains parallel to the c axis (base vector [0 0 1]). The same ketone oxygen atom therefore accepts two hydrogen bonds, one intermolecular and one intramolecular. The hydrogen bond lengths and bond angles are summarized in Table 1. Fig.2 depicts both the intermolecular and intramolecular hydrogen bonds. The length of intermolecular hydrogen bond is 0.303 Å shorter than the sum of the van der Waals radii.

Related literature
Although the length of hydrogen bonds does not necessarily correlate linearly with bond strength, due to packing constraints in the lattice, it is probable that this very short bond is moderate to strong. This is especially likely considering that the bond angle very closely approaches ideality.

Refinement
The positions of all hydrogen atoms bonded to C atoms were calculated using the standard riding model of SHELXL97 (Sheldrick, 2008) with C-H(aromatic) and C-H (methylene) distances of 0.93 Å and U iso = 1.2 U eq , and C-H(methyl) distances of 0.96 Å and U iso = 1.5U eq . The phenolic hydrogen atoms were located in the difference Fourier map and allowed to refine isotropically.
supplementary materials sup-2 Figures Fig. 1. The molecular structure of the title compound with 50% probability ellipsoids. Hydrogen atoms have been rendered as spheres of arbitrary radius.

Special details
Experimental .  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.