noun
- A cation formed by the addition of a proton or other cation to a neutral molecule, especially in organic chemistry.
Usage: chemistry; technical
Examples
- The oxonium ion is a common onium species formed when water accepts a proton.
- In organic synthesis, ammonium salts are onium compounds with nitrogen at the center.
- The formation of an onium intermediate is a key step in many electrophilic addition reactions.
- Sulfonium ions are onium cations containing a positively charged sulfur atom.
- Chemists use onium compounds to understand reaction mechanisms in detail.