Physical and chemical properties of hydroxyflavones. IV. Infrared absorption spectra of dihydroxyflavones containing the 5‐hydroxyl group

Abstract

AbstractSolid state infrared curves (O‐H and C‐H stretching region) are given for 5, n‐dihydroxyflavones, where n is 2′, 3′, 4′, 6, 7 and 8. In chloroform solution spectra of 3,5‐dihydroxyflavone and 3‐hydroxy‐5‐methoxyflavone, the 3‐OH stretching band appears at 3400 and 3334 cm−1, respectively, indicative of a stronger hydrogen bond in the latter substance. Solid state and solution carbonyl bands are presented for twenty‐six flavone derivatives which contain a hydroxyl, methoxyl or acetoxyl group at the 5‐position. The solution spectra (dioxane or carbon tetrachloride) of fourteen flavone derivatives containing a free 5‐hydroxyl group show carbonyl bands at 1655±2 cm−1. Eleven flavones in which the 5‐hydroxyl is blocked (carbon tetrachloride solution) give spectra with flavone carbonyl bands at 1653±3 cm−1. The high resolution chloroform solution spectrum of 3, 5‐dihydroxyflavone possesses a multi‐peaked carbonyl band with midpoint at 1641 cm−1. The chloroform solution spectrum of 3‐hydroxy‐5‐methoxyflavone has a very strong band at 1616 cm−1, with shoulder at 1646 cm−1. Spectral data of this and a previous paper support the postulate that in 4′‐hydroxyflavone the flavone carbonyl oxygen is the donor atom in an intermolecular hydrogen bond. Certain details of synthesis, and analytical data, are given for 3, 5‐dihydroxyflavone.