Coumarin (/ˈkuːmərɪn/) or 2H-chromen-2-one is an aromatic organic chemical compound with formula C9H6O2. Its molecule can be described as a benzene molecule with two adjacent hydrogen atoms replaced by a lactone-like chain −(CH)=(CH)−(C=O)−O−, forming a second six-membered heterocycle that shares two carbons with the benzene ring. It can be placed in the benzopyrone chemical class and considered as a lactone.