N-(2-Methoxyphenyl)phthalamic acid

The title compound, C14H13NO3, adopts a twisted conformation in the crystal, with an interplanar angle between the two benzene rings of 87.30 (5)°. Molecules within the structure are linked via O—H⋯O interactions, forming a hydrogen-bonded chain motif with graph set C(7) along the glide plane in the [001] direction.

The title compound, C 14 H 13 NO 3 , adopts a twisted conformation in the crystal, with an interplanar angle between the two benzene rings of 87.30 (5) . Molecules within the structure are linked via O-HÁ Á ÁO interactions, forming a hydrogenbonded chain motif with graph set C(7) along the glide plane in the [001] direction.

Comment
Molecules of the title compound ( Fig. 1.) exhibit a conformation wherein the interplanar angle between the two phenyl rings is observed to be 87.30 (5)°. The 2-methoxy-substituted ring is in almost perfect alignment with the amide moiety, the interplanar angle between the two being 3.23 (15)°. However, the twisted conformation is due to the almost 90° interplanar angle between the amide and the carboxy-substituted phenyl ring (89.81 (8)°). This conformation is similar to that observed in the structure of N-(2-phenyl)phthalamic acid (Smith et al. 1983;Bocelli et al. 1989). It should also be noted that a more planar conformation is observed where an intramolecular hydrogen bond can be formed between the hydrogen of the amide moiety and a hydrogen bond acceptor at the 2-position of the ring adjacent to the amide carbonyl, as is observed in N-(2-methoxyphenyl)-2-methoxybenzamide (Parra et al. 2001).
An intermolecular hydrogen bond is observed in the interaction between O1, in the carboxylic acid moiety of one molecule (acting as the hydrogen bond donor), and O3, the amide carbonyl of an adjacent molecule (which acts as the acceptor). This O1-H1O···O3 hydrogen bond (1.72 (3) Å) links the molecules along the crystallographic <001> direction (Fig. 2.) and, as a result, the molecules in the chain are related by the glide plane symmetry element along the c axis. It is worth noting that despite the presence of four oxygen atoms, all of which have the potential to act as hydrogen bond acceptors, the amide proton, H1N, does not form a hydrogen bond in this structure; a rare exception to Etter's first rule (Etter, 1990). In this case, a number of weak C-H···O hydrogen bonds form in preference, with the carbon atoms of the aromatic rings and their associated protons acting as the hydrogen bond donors.
Within the molecule itself, there are four distinct oxygen atom environments. The carboxylic acid oxygen atoms, O1 and O2, exhibit bond lengths to the carbon atom of the acid group within two standard deviations of the International Tables for Crystallography value (Allen et al. 2006) demonstrating distinct single and double bond character respectively. This suggests very little resonance-related charge seperation across the carboxylic acid group in this molecule. The same cannot be said of the amide moeity, however, as the carbonyl bond is longer in this case due to resonance between O3 and N1. This is a far from unexpected development as the C8-O3 bond length is close to the average for bonds of this type.
There is no resonance form for this molecule associated with a change in the bond lengths to O4 and hence these bond lengths are also in agreement with the International Tables for Crystallography values.

Experimental
N-(2-methoxyphenyl)phthalamic acid was obtained from Sigma-Aldrich. Crystals suitable for single-crystal X-ray crystallography were grown via evaporation of the solvent from a solution of the product in methanol.

Refinement
H atoms were located from the Fourier difference map of electron density and refined freely. The most disagreeable reflections were omitted; three reflections exhibiting a Δ(F 2 ) value greater than 5 su were removed.

Figure 1
The asymmetric unit of the title compound with displacement ellipsoids drawn at the 50% probability level.  View of the C(7) hydrogen bond (dashed lines) motif in the [001] direction in the structure of the title compound.
Carbon-bonded hydrogen atoms are omitted for clarity. Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.