2-(2,7-Dimethoxy-1-naphthoyl)benzoic acid

In the title compound, C20H16O5, the dihedral angle between the naphthalene ring system and the benzene ring is 67.43 (5)°. The bridging carbonyl C—C(=O)—C plane makes dihedral angles of 82.64 (6) and 41.79 (7)°, respectively, with the naphthalene ring system and the benzene ring. The dihedral angle between the carboxy O—C(=O)—C plane and the benzene ring is 36.38 (7)° and that between the bridging carbonyl C—C(=O)—C plane and the carboxy O—C(=O)—C plane is 51.88 (8)°. The crystal structure is stabilized by intermolecular O—H⋯O and C—H⋯O hydrogen-bonding interactions. An intramolecular C—H⋯O hydrogen bond occurs between a naphthalene H atom and the carbonyl O atom of the carboxy group.


Comment
In the course of our study on electrophilic aromatic aroylation of 2,7-dimethoxynaphthalene, peri-aroylnaphthalene compounds have proven to be formed regioselectively with the aid of suitable acidic mediators (Okamoto & Yonezawa, 2009).
As a part of our continuing study on the molecular structures of these homologous molecules, the crystal structure of title compound, 1-monoaroylnaphthalene bearing carboxy group, is discussed in this report.

Refinement
All H atoms were found in a difference map and were subsequently refined as riding atoms, with C-H = 0.93 (aromatic) and 0.96 (methyl) Å, and with U ĩso (H) = 1.2U eq (C). Fig. 1. The molecular structure, showing the atom-labeling scheme and 50% probability displacement ellipsoids. The intramolecular C-H···O interaction is shown as a dashed line.

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 > σ(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.