# Quaternary compound

Quaternary ammonium cation. The R's may be the same or different groups. They may also be connected (cyclic).

In chemistry, a quaternary compound is a cation consisting of a central positively charged nitrogen group atom with four substituents, especially organic (alkyl and aryl) groups, discounting hydrogen atoms.[1]

The best known quaternary compounds are quaternary ammonium cations, having a nitrogen atom at the centre.[2] For example, in the following reaction, the nitrogen atom is said to be quaternized as it has gone from 3 to 4 substituents:

$\mathrm{R_3N + RCl \longrightarrow R_4N^+ \ Cl^-}$

Other examples include substituted phosphonium salts (R4P+), substituted arsonium salts (R4As+) like arsenobetaine, as well as some arsenic containing superconductors.[3] Substituted stibonium (R4Sb+)[4] and bismuthonium salts (R4Bi+) have also been described.[5]