Quaternary compound

File:Quaternary ammonium cation.svg

Quaternary ammonium cation. The Rs may be the same or different groups. (The Rs may also be connected, making a cyclic ion.)

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 center. For example, in the following reaction, the nitrogen atom is said to be quaternized as it has gone from 3 to 4 substituents:

$\mathrm{R}{\phantom{A}}_3\mathrm{N}+\mathrm{R}\mathrm{C}\mathrm{l}⟶\mathrm{R}{\phantom{A}}_4\mathrm{N}{\phantom{A}}^{+}\mathrm{C}\mathrm{l}{\phantom{A}}^{-}$

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

See also

• Binary compound
• Ternary compound
• Onium ion
• Quaternary phase