Crystal structures of dihydroquercetin 3-acetate and dihydroquercetin 3,3',4',7-tetraacetate: Hydrogen bonding in 5-hydroxyflavanones

The molecular structures of dihydroquercetin 3-acetate 3 and dihydroquercetin 3,3'.4',7-tetraacetate 4 were determined by single crystal X-ray analysis. Comparison of their crystal data with those, of 16 known 5-hydroxyflavanones shows intramolecular O(5)-H - O(4)=C hydrogen bonding, preference for nearly perpendicular orientation of the two aromatic rings and preferred sofa conformation of the heterocyclic ring. The major stabilizing force in the crystal packing pattern of 3 is intermolecular hydrogen bonding.