The crystal structure of an unusual chromophoric dimeric furan.

The red-orange crystals of (E)-2-[1-(3-hydroxy-2-furanyl)ethylidene]-(2H)-furan-3-one, C10H8O4, crystallize in space group P2(1)/c with Z = 8, cell dimensions at 123 K [293 K], a = 16.222(4) [16.360(8)] A, b = 7.089(2) [7.219(4)] A, c = 16.631(5) [16.722(8)] A, beta = 115.20(3) [115.50(7)]degrees. There are two symmetry nonequivalent molecules in the unit cell, each of which has an unsymmetrical configuration with an unsymmetrical O-H...O = C intramolecular hydrogen bond. This is contrary to a previous report based on the solid-state i.r. spectrum. The two furan rings in each molecule are planar, but not coplanar. They are inclined at angles of 33.4 degrees and 26.1 degrees to each other, in opposite senses in the two molecules.