A retrochalcone is a chalcone-like compound in which the normally present hydroxy groups at the 2' and 6' positions are missing. The retrochalcone structure has a propenal bridge connected to two benzene rings at each end. The ring closest to the oxygen, is labelled with primed numbers, normally with a hydroxy group at the 4' position. This is the A ring. The ring closest to the double bond is numbered with simple digits starting from 1 at the bridge connection. This is the B ring. There is usually a hydroxy group at the 4 position. The retrochalcones are found naturally where they are derivatives of flavones. Retrochalcones can be classed as minor flavinoids.