A single heteroatom, for example, –Cl and =O; a heteroatom bearing one or more hydrogen atoms or other heteroatoms, for example, –NH₂, –OH, –SO₃H, –PO₃H₂ and IO₂; or a heteroatomic group attached to or containing a single carbon atom, for example, –CHO, –C≡N, –COOH and –NCO, attached to a parent hydride.