Intermediate Topic 765 of 1102 Organic Chemistry
Carbanions
Negatively charged carbon species stabilized by electron-withdrawing groups.
In-depth explanation of Carbanions
A carbanion is a species in which a carbon atom carries a negative charge and a lone pair, with three bonds and a pyramidal geometry. The stability order is the opposite of carbocations: methyl is most stable, followed by primary, secondary and tertiary, because alkyl groups destabilize the extra electron pair. Carbanions are stabilized by electron-withdrawing groups and by resonance delocalization, which spreads the negative charge onto electronegative atoms. They behave as strong bases and as nucleophiles in carbon-carbon bond formation.
Going deeper: Carbanions
Key ideas: Carbon with three bonds and a lone pair, pyramidal sp3 (or planar when conjugated). Stability is opposite to carbocations: methyl > 1 > 2 > 3, and more s character helps: sp (alkynyl) > sp2 > sp3. Stabilised by adjacent C=O, NO2, CN or an aromatic ring. Used as nucleophiles in Grignard, aldol and Claisen reactions. Strong bases such as NaNH2 and organolithiums produce them.
Common mistakes and connections: Students think a carbanion is stabilised by alkyl groups the way carbocations are; it is destabilised. Another error is assuming Grignard reagents are free carbanions; they are polar covalent C-Mg bonds. Links to acidity of alpha hydrogens, enolates and carbon-carbon bond formation.
Visualization of Carbanions
A carbanion lone pair in an orbital with more s-character is held closer to the nucleus and more stable, so sp carbanions are the most stable. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Enolate ions are carbanion-like species stabilized by resonance onto the oxygen of a carbonyl group.
Frequently asked questions about Carbanions
What is Carbanions?
Negatively charged carbon species stabilized by electron-withdrawing groups.
Is Carbanions a beginner, intermediate or advanced topic?
Carbanions is a intermediate topic in Organic Chemistry. It builds on the vocabulary of beginner topics in this area.
What should I learn before Carbanions?
Study these earlier topics in Organic Chemistry first: Electromeric Effect, Free Radicals, Carbocations.
What comes after Carbanions?
The next topics in Organic Chemistry are Carbenes and Homolytic and Heterolytic Fission.
Can I practise Carbanions with quizzes?
Yes. The interactive lesson includes a self-check question on Carbanions, and the Organic Chemistry quiz draws on every topic in this area.
Where Carbanions fits in Organic Chemistry
Carbanions is topic 37 of 148 in Organic Chemistry.