Quaternary compound
In chemistry, a quaternary compound is a compound consisting of exactly four chemical elements.
In another use of the term in organic chemistry, a quaternary compound is or has a cation consisting of a central positively charged atom with four substituents, especially organic groups, discounting hydrogen atoms.
The best-known quaternary compounds are quaternary ammonium salts, having a nitrogen atom at the centre. For example, in the following reaction, the nitrogen atom is said to be quaternized as it has gone from 3 to 4 substituents:
Other examples include substituted phosphonium salts, substituted arsonium salts like arsenobetaine, as well as some arsenic-containing superconductors. Substituted stibonium and bismuthonium salts have also been described.
