Electronic structure of chromone and its hydroxylated derivatives on positions 2 and 3

The electronic structure of chromone (1) and those of its 2-hydroxy (2) and 5-hydroxy (3) derivatives were studied by semiempirical and ab initio molecular orbital methods. Several electronic parameters show that the A-ring is an aromatic system, whereas the C-ring does not present conjugation. In the C-ring, the double bonds are located in the carbonyl group and between C(2)-C(3). These results were confirmed by comparison with geometries of chromone derivatives which were determined by X-ray diffraction data. The relative stability of compounds (2) and (3) was explained and the sites of acid, basic, nucleophilic and electrophilic attack were also determined. (C) 1998 Elsevier Science B.V.