Discreet units of atoms with special physical and/or chemical properties are known as functional groups. More than one double bond or triple bond can be incorporated into organic molecules. Many naturally occurring compounds in nature have double or triple bonds. Terpenes are cyclic and acyclic compounds with the formula that are usually found in plants. Hemiterpenes consist of one isoprene unit. Isoprene itself is the only hemiterpene, but oxygen-containing derivatives are hemiterpenoids. Functional groups are collections of atoms that impart unique physical and chemical characteristics to a molecule. The amine-bearing carbon is the locant and must be part of the longest hydrocarbon chain. The nomenclature systems for an aldehyde and a ketone are slightly different.