5,6,7,8-Tetrahydroquinolin-8-one

In the quinoline fused-ring system of the title compound, C9H9NO, the pyridine ring is planar to within 0.011 (3) Å, while the partially saturated cyclohexene ring adopts a sofa conformation with an asymmetry parameter ΔC s(C6) = 1.5 (4)°. There are no classical hydrogen bonds in the crystal structure. Molecules form molecular layers parallel to (100) with a distance between the layers of a/2 = 3.468 Å.

In the quinoline fused-ring system of the title compound, C 9 H 9 NO, the pyridine ring is planar to within 0.011 (3) Å , while the partially saturated cyclohexene ring adopts a sofa conformation with an asymmetry parameter ÁC s (C6) = 1.5 (4) . There are no classical hydrogen bonds in the crystal structure. Molecules form molecular layers parallel to (100) with a distance between the layers of a/2 = 3.468 Å .
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: JH2281).  (Kelly & Lebedev, 2002) and a key substrate to synthesis of its 8-amino substituted derivatives with pharmacological activity (e.g. Gudmundsson et al., 2009). As a part of our ongoing study on the synthesis and structure of condensed pyridine and quinoline derivatives (Lipińska, 2005;Karczmarzyk et al., 2010) we report herein the X-ray structure of the title compound. This compound is well-known on organic chemistry but its crystal structure is not current in the Cambridge Structural Database (November 2010 Release; Allen, 2002;Bruno et al., 2002).
There are no classical hydrogen bonds in the crystal structure of (I). The nearly planar molecules form molecular layers parallel to (100) crystallographic plane (Fig. 2) imposing in the unit cell the pseudo-mirror plane passing through N, O, C(sp 2 ) and C5(sp 3 ) atoms (higher pseudosymmetry Pnma space group). The distance between neighbouring planes of a/2 = 3.468 Å is comparable to a van der Waals distance of about 3.5 Å for the π-π interacting aromatic skeletons of pyridine rings.

Refinement
The H atoms were positioned geometrically and treated as riding on their C atoms, with C-H distances of 0.93 (aromatic) and 0.97 Å (CH 2 ), and were refined with U ĩso (H) values of 1.5U eq (C). The Flack parameter originally was refined to 0.4 (6), which is essentially indeterminate. For this reason, the Friedel equivalents were merged using MERG4 in SHELXL97 (Sheldrick, 2008) and the absolute structure was arbitrarily assigned. The PLATON symmetry check (Spek, 2009) Fig. 1. The molecular structure of (I), with atom labels and 30% probability displacement ellipsoids for non-H atoms.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.