the group of atoms responsible for the characteristic reactions of a compound. The functional group is –OH for alcohols, –CHO for aldehydes, –COOH for carboxylic acids, etc., an atom, or a group of atoms that has similar chemical properties whenever it occurs in different compounds. It defines the characteristic physical and chemical properties of families of organic compo, orgaanilise ühendi molekuli osa (aatom või aatomirühm), mis määrab ühendi kuulumise mingisse kindlasse klassi ning millest sõltuvad tema keemilised omadused (nt hüdroksüülrühm)