Crystal structure of 2-(5-meth-oxy-1-benzo-furan-3-yl)acetic acid.

The benzo-furan residue in the title compound, C11H10O4, is essentially planar (the r.m.s. deviation for the nine non-H atoms = 0.011 Å). While the meth-oxy group is coplanar with the fused ring system [C-C-O-C torsion angle = 3.1 (3)°], the acetic acid residue occupies a position almost prime [C-C-C-C = 77.0 (2)°]. In the crystal, centrosymmetrically related mol-ecules are linked by O-H⋯O hydrogen bonds to form eight-membered {⋯HOCO}2 synthons. The dimeric aggregates assemble into supra-molecular layers in the ab plane via benzene-C-H⋯O(ring) inter-actions.