Originally, the compound betaine, $\ce{(CH3)3N^{+}–CH2C(=O)O^{−}}$ $N,N,N$-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.