2′-Acetonaphthone

In the structure of the title compound [systematic name: 1-(naphthalen-2-yl)ethanone], C12H10O, the acetyl group is approximately coplanar with the naphthalene ring with a Car—Car—C=O torsion angle of 5.8 (2)°. In the crystal, the molecules are packed in a classic herringbone arrangement typical for aromatic polycycles such as pentacene. They are also linked by weak end-to-end C—H⋯O interactions along the ac diagonal.

In the structure of the title compound [systematic name: 1-(naphthalen-2-yl)ethanone], C 12 H 10 O, the acetyl group is approximately coplanar with the naphthalene ring with a C ar -C ar -C O torsion angle of 5.8 (2) . In the crystal, the molecules are packed in a classic herringbone arrangement typical for aromatic polycycles such as pentacene. They are also linked by weak end-to-end C-HÁ Á ÁO interactions along the ac diagonal.   Table 1 Hydrogen-bond geometry (Å , ).  shown to be quite flexible and fit guests of differing size, in part by also incorporating varying numbers of hydrogenbonded water molecules. This adaptability of the host lattice has been described as permitting "induced fitting" of guest molecule(s). The cephradine host molecules fully surround their guests and keep individual molecules of (I) separated by the b axis distance of 7.1965 (3) Å. In the second example (refcode: NECPUG), (I) forms into π-stacks which fill channels that run along the c axis of a lattice formed from the modified bile acid derivative 3-epiursodeoxycholic acid (Miyake et al., 1998). The average separation of molecules of (I) along these channels is 3.51 Å, just 0.1 Å greater than the sums of the van der Waals radii of two carbon atoms. Both of these structures for (I) have very poor precision in the interatomic distances with mean s.u. of 0.01 Å.

Related literature
We have therefore determined the crystal structure at 173 K of pure (I). Fig. 1 displays the molecular structure as found in the crystal lattice. The acetyl group is approximately co-planar with the naphthalene ring and the carbonyl oxygen is anti to the ring with the torsion angle C1-C2-C11-O1 174.8 (1)°. By comparison, in NECPUG the oxygen atom is in the syn position. The disorder in MEGXUR precludes a definitive conformational assignment, but the major component appears to have the oxygen anti as in (I). It is instructive to compare the bond distances determined for pure (I) with those determined in the host lattices. The high-accuracy structure reported here may also be used to define rigid templates as an aid in refining future inclusion compounds of (I).
In contrast to the host-guest complexes MEGXUR, which has isolated molecules of (I), and NECPUG with π-stacked (I), the crystal packing of pure (I) is of the herringbone 2-D edge-to-face type ( Figure 2). This arrangement of crystal packing is reminiscent to that found in pentacene as determined at 90 K (Mattheus et al., 2001). Unlike pentacene, molecules of (I) are also linked by weak end-to-end by C8-H8···O1 intermolecular interactions (Table 1).

Experimental
A sample of (I) was prepared by the method of Bassilios and Salem (1952).

Refinement
Hydrogen atoms attached to carbon were treated as riding, with C-H = 0.98 Å and U iso (H) = 1.5U eq (C) for methyl and C -H = 0.95 Å and U iso (H) = 1.2U eq (C) for aromatic H atoms.

Figure 1
Molecular structure of (I) drawn with displacement elipsoids at the 50% probability level and showing the atom numbering scheme.

Figure 2
An extended packing diagram viewed down the c* direction, showing the "herringbone" edge-to-face packing arrangements. Only atoms involved in short contacts to neighbouring atoms are labelled [Sym. codes: (i) -x + 3/2, y + 1/2, -z + 1/2; (ii) -x + 3/2, y -1/2, -z + 1/2; (iii) -x + 1/2, y -1/2, -z + 1/2; (iv) -x + 1/2, y + 1/2, -z + 1/2]. The O1···H8-C8 Hbonds are not shown but are oriented along the ac diagonal (approximately perpendicular to the page).  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.25 e Å −3 Δρ min = −0.23 e Å −3 Special details Experimental. A crystal coated in Paratone (TM) oil was mounted on the end of a thin glass capillary and cooled in the gas stream of the diffractometer Kryoflex device. 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.