2H-Chromen-4(3H)-one

In the title compound, C9H8O2, a benzo-annulated heterocyclic ketone, the non-aromatic six-membered ring adopts an E 2 conformation. In the crystal, C—H⋯O contacts connect the molecules into double sheets perpendicular to the crystallographic a axis. The centroid–centroid distance for two π-systems is 3.7699 (6) Å.


Comment
In general, saturated, six-membered carbocycles and heterocycles adopt energetically favourable chair-or boat-conformations in solution and in the solid state although a variety of other conformations such as half-chair-or twist-forms are available. The annulation of aromatic rings can influence the conformation of such ring-systems and "freeze" one of the less common conformations. In our continued interest in effects of substituents and annulation of differently-substituted aromatic systems on the conformation of six-, seven-and eight-membered ring systems, we determined the crystal structure of the title compound to enable comparative studies. As of today, only one structural analysis of a chromium(0)-compound featuring the title compound as a ligand is apparent in the literature (Stewart et al. 1984).
The heterocyclic six-membered ring adopts an E 2 conformation with carbon atom C1 acting as the envelope-atom. The latter one is displaced by 0.337 (1) Å from the least-squares plane defined by the atoms of the heterocycle. The least-squares planes defined by the carbon atoms of the phenyl ring as well as the skeletal atoms of the heterocycle intersect at an angle of 7.73 (6)°.
In the crystal structure, C-H···O contacts whose ranges fall by about 0.2 Å below the sum of van-der-Waals radii of the atoms participating are observed. These include both H atoms of the methylene group in ortho-position to the intracyclic O atom as donor atoms and exclusively the O atom of the carbonyl group as acceptor (Fig. 2). In total, the molecules are connected to double layers perpendicular to the crystallographic a axis. In terms of graph-set analysis (Etter et al., 1990;Bernstein et al., 1995) the descriptor for these contacts on the unitary level is C(5)C(5). The shortest C g ···C g -distance for two π-systems was measured at 3.7699 (6) Å.
The packing of the title compound is shown in Figure 3.

Experimental
The compound was obtained commercially (Aldrich). Crystals suitable for the X-ray diffraction study were taken directly from the provided product.

Refinement
Carbon-bound H-atoms were placed in calculated positions (C-H 0.95 Å for aromatic C atoms and C-H 0.99 Å for aliphatic C atoms) and were included in the refinement in the riding model approximation, with U(H) set to 1.2U eq (C).