Originally, the compound betaine,
-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.
PAC, 1995, 67, 1307
(Glossary of class names of organic compounds and reactivity intermediates based on
structure (IUPAC Recommendations 1995))
on page 1322