Quaternary compound
# 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 (alkyl and aryl) 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:

    ${\ce {R3N + RCl -> R4N+Cl-}}$

Other examples include substituted phosphonium salts $(R_4P^+),$ substituted arsonium salts $(R_4As^+)$ like arsenobetaine, as well as some arsenic-containing superconductors. Substituted stibonium $(R_4Sb^+)$ and bismuthonium salts $(R_4Bi^+)$ have also been described.

