2-(4-Formyl-2,6-dimethoxyphenoxy)acetic acid

In the title compound, C11H12O6, the aldehyde group is disordered over two sites in a 0.79:0.21 ratio. The carboxylic acid chain is found in the [ap,ap] conformation due to two intramolecular O—H⋯O hydrogen bonds.

In the title compound, C 11 H 12 O 6 , the aldehyde group is disordered over two sites in a 0.79:0.21 ratio. The carboxylic acid chain is found in the [ap,ap] conformation due to two intramolecular O-HÁ Á ÁO hydrogen bonds.

Comment
The title compound was synthesized as a precursor for asymmetric PPV-type [poly(p-phenylene vinylene)] oligomers. These compounds are promising candidates as the active materials in organic memories (Bandyopadhyay & Pal, 2003) and as nonlinear optical (NLO) materials with a high first-order hyperpolarizability (Chemla, 1987). Besides the condition that these oligomers should bear acceptor and donor substituents connected by a π-system, it is of critical importance for their usefulness as an NLO material and as a bistable organic memory material that the crystal packing is non-centrosymmetric.
In particular, the compound should crystallize in a polar space group. To engineer the crystal packing in order to meet this criterion, it is necessary to introduce certain statistically well chosen synthons (Desiraju, 1997). Therefore, we opted for carboxylic acid functional groups (powerful hydrogen bond donors) in the basic structure of the organic semiconductors. To combine the electronic (A-π-D) and the structural (non-centrosymmetric space group) requirements, we used the Williamson ether synthesis to prepare the title compound as a building block for a PPV-based semiconductor bearing a carboxylic acid moiety.
The carboxylic acid moiety is found in the [ap,ap] conformation ( Fig. 1): the carboxyl H atom points in the opposite direction of the carbonyl group and the O4-C41-C42-O41 torsion angle is -168.64 (19)°. The reason for this unexpected conformation is the presence of an intramolecular bifurcated hydrogen bond involving H42, O4 and O5 (Table 1 and Fig. 2).
Indeed, Lide showed, based on microwave experiments on gaseous formic acid, that, in general, the sp conformer is more stable than the ap conformer by about 16 kJ mol -1 (Lide, 1964). The acetic acid chain is twisted out-of-plane by about 113°a nd the torsion angle O4-C41-C42-O42 is about 11°.

Refinement
The aldehyde moiety proved to be orientationally disordered over two sites in a 79:21 ratio (refined values 0.785 (6):0.215 (6)). The structure was initially refined with the aldehyde group in one position and then the second site was located in the residual electron density map. For the two aldehyde functions, consisting of three atoms, O11A and O11B were restrained to have the similar anisotropic displacement parameters, and the C1-C11A/C1-C11B and C11A-O11A/ C11B-O11B distances were restrained to be equal. C11A and C11B were constrained to posses identical anisotropic displacement parameters. H atoms H11A and H11B were placed on the geometrically calculated positions and refined as 'riding'. Fig. 1. Molecular structure of the title compound with the numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are represented as spheres with an arbitrary radius.