betaines

https://doi.org/10.1351/goldbook.B00637

Originally, the compound betaine,

(CH₃)₃N⁺–CH₂C(=O)O⁻

N,N,N-trimethylammonioacetate, and similar zwitterionic compounds derived from other amino acids. By extension, neutral molecules having charge-separated forms with an onium atom which bears no hydrogen atoms and that is not adjacent to the anionic atom. Betaines cannot be represented without formal charges. E.g.

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See also: dipolar compounds, mesoionic compounds, ylides, zwitterionic compounds

Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1322 (https://doi.org/10.1351/pac199567081307)