Crystal structure of 9-methacryloylanthracene

In the title compound, the substituted aromatic C atom lies 0.2030 (16) Å out of the anthryl plane, which forms a dihedral angle 88.30 (3)° with the plane of the transoid methacryloyl moiety.

In the title compound, C 18 H 14 O, with systematic name 1-(anthracen-9-yl)-2methylprop-2-en-1-one, the ketonic C atom lies 0.2030 (16) Å out of the anthrylring-system plane. The dihedral angle between the planes of the anthryl and methacryloyl moieties is 88.30 (3) and the stereochemistry about the Csp 2 -Csp 2 bond in the side chain is transoid. In the crystal, the end rings of the anthryl units in adjacent molecules associate in parallel-planar orientations [shortest centroid-centroid distance = 3.6320 (7) Å ]. A weak hydrogen bond is observed between an aromatic H atom and the O atom of a molecule displaced by translation in the a-axis direction, forming sheets of parallel-planar anthryl groups packing in this direction.

Chemical Context
Enolizable aldehydes react with formaldehyde in strong aqueous base to form polyols, whereas ketones usually react to form polyhydroxyketones (Davidson & Bogert, 1935;Vik et al., 1973;Weissermel & Arpe, 1997;Wittcoff et al., 2013). Therefore, the observed methylation of 9-acetylanthracene by formaldehyde with alcoholic potassium carbonate (see Scheme below) is remarkable in that the reaction occurs with weak base in a non-aqueous medium by reduction of formaldehyde to form the methyl group (Pande et al., 1998). Consequently, we obtained an X-ray structure determination to confirm the identity of the isolated product, 9-methacryloylanthracene or 1-(9-anthryl)-2-methyl-2-propen-1-one.

Structural commentary
The crystal structure (Fig. 1) establishes the material to be the -methylated aldol condensation product. Bond distances and valence angles agree well between the observed and the calculated structures. The anthryl ring system is essentially planar, as is the methacryloyl substituent (excepting the hydrogen atoms of the methyl group), whereas the calculated structure shows a slight deviation, about 7 , of the methacryloyl skeleton from planarity. The substituted C atom (C9) of the anthryl group also lies in the plane of the substituent, deviating by only 0.002 (2) Å . However, this C atom is puckered, so that the carbonyl C atom resides 0.2030 (16) Å out of the anthryl plane. This puckering is absent in the calculated structure. The planes of the anthryl and methacryloyl moieties are nearly perpendicular with a dihedral angle of 88.30 (3) (but about 12 from perpendicular in the calculated structure). This general orientation is demanded by the close intramolecular approach of the methacryloyl group to the peri-H atoms (H1 and H8), but packing effects may also contribute to deciding the exact angle since that calculated for the energy minimum differs by about 10 from that observed. The observed positioning is not quite symmetrical, with C11 being slightly closer (0.018 Å ) to H1 than to H8. Similar geometries are found in 9-acetylanthracene, with a dihedral angle of 88.70 (3) (Andersson et al., 1984) and in 9-(bromoacetyl)anthracene, with a dihedral angle of 74.2 (1) (Kubo et al., 2007). Unfavorable non-bonded interactions in the present structure are likely the reason that the methyl group, which is bulkier than the methylene group, projects away from the anthryl moiety, making the stereochemistry of the C11-C12 bond transoid. The puckering observed at C9 would partially relieve these unfavorable steric interactions occurring about this position.

Supramolecular_features
Intermolecular close contacts between large aromatic groups in the solid state often involvestacking interactions involving parallel planar associations (Głó wka et al., 1999). This motif is observed here as well, with the anthryl rings displaced and stacking alternately with those of neighboring molecules (Fig. 2). The centroid-centroid separations are 3.6320 (7) and 3.7532 (7)  ORTEP (30% probability elipsoids) plot of the title compound showing the atom-labeling scheme. Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
Views parallel to the planes of both the anthryl and the methacryloyl moieties (top) and parallel to the methacryloyl but perpendicular to the anthryl with H atoms omitted for clarity (bottom).

Figure 3
A fragment of a [100] hydrogen-bonded chain of molecules in the crystal showing the intermolecular OÁ Á ÁH close contact (dotted line). (Table 1), resulting in the formation of anthryl groups packing in parallel-planar sheets in this direction.

Synthesis and crystallization
Refluxing 9-acetylanthracene (1.0 g), paraformaldehyde (273 mg), and potassium carbonate (942 mg) in 3.0 ml ethanol afforded 80 mg product which eluted first from an alumina column with 10% ethyl acetate-hexane and was crystallized from chloroform-hexane in the form of colorless plates.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The H atoms were placed in calculated positions and refined as riding atoms, with C-H = 0.95 Å and U iso (H) = 1.2U eq (C-alkene and C-aromatic), and C-H = 0.98 Å and U iso (H) = 1.5 U eq (C-methyl).

Calculations
Density-functional theoretical computations were performed using Gaussian software (Frisch et al., 2010) through the Ohio Supercomputing Center (in Columbus OH) with Zhao and Truhlar's hybrid meta exchange-correlation functional, M06-2X, (Choe, 2012;Huh & Choe, 2010;Zhao & Truhlar, 2008), which is parameterized for non-metallic systems with noncovalentinteractions for accurate modelling of intramolecular dispersion effects. The basis set used is 6-31+G(d). To obtain the geometry at the global minimum potential energy, optimization was based on the minimum-energy conformation from a two-torsion MM2 plot (ChemBio3D Ultra 12.0; www.CambridgeSoft.com) using rotations about the C9-C11 and C11-C12 single bonds. The M06-2X structure has all vibrational frequencies positive, verifying that it is at a potential-energy minimum. Calculated values for geometrical paramters in the optimized isolated molecule are given in the Supporting information. Data collection: APEX2 (Bruker, 1997); cell refinement: SAINT (Bruker, 1997); data reduction: SAINT (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXS97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

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.