Illustrated Glossary of Organic Chemistry

Quaternary ammonium salt (4^o ammonium salt): An ammonium salt in which the nitrogen atom bearing the +1 formal charge has four carbon-nitrogen single bonds (i.e., it is bonded to four carbon groups).

Methylammonium chloride A primary (1o) ammonium salt		Dimethylammonium chloride A secondary (2o) ammonium salt		Trimethylammonium chloride A tertiary (3o) ammonium salt		Tetramethylammonium chloride A quaternary (4o) ammonium salt		1,1-diphenylpyrrolidinium bromide A quaternary (4o) ammonium salt