In chemistry, peroxides are a group of compounds with the structure R−O−O−R, where the R's represent a radical (a portion of a complete molecule; not necessarily a free radical[1]) and O's are single oxygen atoms.[2][3] Oxygen atoms are joined to each other and to adjacent elements through single covalent bonds, denoted by dashes or lines. The O−O group in a peroxide is often called the peroxide group, though some nomenclature discrepancies exist. This linkage is recognized as a common polyatomic ion, and exists in many molecules.