Heteroatoms and functional groups are known collectively as "substituents", as they are considered to be a substitute for the hydrogen atom that would be present in the parent hydrocarbon of the organic compound in question.
Heteroatomer og funktionelle grupper betegnes under et som substituenter, da de betragtes som værende en erstatning af det hydrogenatom, der ellers ville have været fastgjort til det pågældende kulstofatom i den organiske forbindelse.