Carbanion

Part of speech: noun

Definitions

1. A negatively charged organic ion in which a carbon atom carries a lone pair of electrons and a formal negative charge
2. An anion centered on carbon, bearing an unshared electron pair that makes it a strong nucleophile in organic reactions
3. The reactive species formed when a carbon atom in an organic molecule gains a negative charge through electron pair retention

Etymology: Carbanion is a plain technical coinage, built from two pieces: "carb-", from carbon, and "anion", the negatively charged ion. The second part carries the older history. "Anion" was formed from the Greek "anion", the present participle of "ienai", meaning "to go", with the prefix "ana-", "up". The name was chosen because anions travel toward the positive electrode, or anode, during electrolysis, so the ion literally "goes up". Michael Faraday coined the term for this reason, which gives the word a more concrete origin than its chemical sound suggests. A carbanion, then, is an anion with a negative charge sitting on a carbon atom. Chemists use the term for a specific class of reactive species, and the name simply stacks the carbon element onto the older ion vocabulary. Since carbanion was formed by combining two existing parts, its meaning follows directly from them.