Structure, tautomerism, and features of 1-(5-acetyl-2,4-dihydroxyphenyl)-3-(furan-2-yl)prop-2-en-1-one (FC) and 1,1′-(4,6-dihydroxybenzene-1,3-diyl)bis[3-(furan-2-yl)prop-2-en-1-one] (FDC)

Quantum chemistry studies of various tautomeric/rotameric forms of the furanyl analogues of acetyl dihydroxychalcone (FC) and dihydroxydichalcone (FDC) have shown that the thermodynamically most stable molecules are planar. In the crystalline solid phase, both molecules are more (FDC) or less (FC) non-planar. Two relatively strong intramolecular H-bonds, whose existence is evidenced by X-ray, computational, and spectral investigations, stabilize the planar geometry and influence the features of the lowest energy tautomers/rotamers of both compounds. Extending to the visible region, the electronic absorption of FC and FDC is accompanied by an intramolecular electron density shift, a property that could have analytical implications.