Derivatives of ammonium compounds,
(NH4+)Y−, in which all four of the hydrogens bonded to nitrogen have been replaced with hydrocarbyl groups. Compounds having a carbon-nitrogen double bond (i.e.
R2C=N+R2Y−) are more accurately called iminium compounds. e.g.
[(CH3)4N]+OH−, tetramethylammonium hydroxide.
See: onium compounds
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1361 (https://doi.org/10.1351/pac199567081307)