carbanions

A carbanion is a chemical species in which a carbon atom bears a negative charge, making it a carbon-centered anion. Carbanions are typically generated by deprotonation of hydrocarbons or by converting a C–H or C–X bond into a carbanionic center, often in the presence of a metal counterion. Bare carbanions are highly reactive and short-lived in solution, so they are usually prepared and studied as metal salts (for example lithium, sodium, or potassium carbanionates) or as stabilized forms such as enolates.

Stabilization of carbanions is a central theme in their chemistry. Delocalization of the negative charge through adjacent π systems or electron-withdrawing substituents reduces basicity and increases lifetime. Classic stabilized carbanions include enolates formed by deprotonation at the α-position of ketones or aldehydes, as well as anions adjacent to esters, nitriles, or sulfones (malonates, cyanoalkyls, etc.). Less stabilized, or non-stabilized, carbanions (such as simple primary alkyl carbanions) are typically more reactive and harder to isolate.

In synthesis, carbanions act as strong bases and versatile nucleophiles. They enable carbon–carbon bond formation through alkylation, acylation, and various conjugate or Michael-type additions. Their reactivity is highly dependent on the surrounding substituents and the solvent; polar aprotic media (such as THF or DME) at low temperature are common, and strong bases like lithium diisopropylamide (LDA) or butyllithium are frequently employed.

Carbanion chemistry underpins many organosynthetic strategies, including enolate chemistry, alkylations, and the construction of complex molecular frameworks.