Definition of betaines

1. Originally, the compound betaine, (CH3)3N+CH2C(=O)O- N,N,N-trimethylammonioacetate, and similar zwitterionic compounds derived from other amino acids. NOC Rule C-816.1, footnote. 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. See also dipolar compounds, mesoionic compounds, ylides, zwitterionic compounds. E.g. (CH3)3P+CH2S(=O)2O-, (Ph)3P+CH2CH2O-