2',6'-Dihydroxyflavone and a New Polymorph of 2'-Hydroxyflavonol

Abstract

The structure of 2'-hydroxyflavonol [3-hydroxy-2-(2-hydroxyphenyl)-4H-1-benzopyran-4-one, C 15 H 10 O 4 ] has been described in the triclinic system [Iinuma, Tanaka, Ito & Mizuno (1987). Chem. Pharm. Bull. 35, 660-667]. We describe here a new polymorph which crystallizes in the monoclinic system. The conformation, characterized by the torsion angle between the γ-benzopyrone moiety and the phenyl ring, is very similar to that described for the triclinic system. The conformation of 2',6'-dihydroxyflavone [2-(2,6-dihydroxyphenyl)-4H-1-benzopyran-4-one, C 15 H 10 O 4 ] is determined by intermolecular hydrogen bonds. Hydroxyl groups by two sets of hydrogen bonds, with the O(2')-H group bonding to the carbonyl group of a neighbouring molecule along the b axis and the O(6')-H group bonding to the O(2') atom of a molecule located in the ab plane.