The 13C NMR spectra of polyhydroxyflavones were systematically examined by using about 70 examples which have a 4-methoxyphenyl B-ring, such as 5, 6, 7-, 5, 7, 8 and 5, 6, 8- trioxygenated and 5, 6, 7, 8-tetraoxygenated flavones and flavonols, and the following results were obtained. In the 13C NMR spectra of flavones, the signals at the 2-, 3-and 4- positions in the C-ring were hardly affected by the substituents on the A-ring except for ...
