Heterolytic Cleavage - Carbanion

Description:

Heterolytic cleavage resulting in carbon with negative charge is called carbanion.

It has sp³ hybridization and tetrahedral structure.

Although it has 8 e⁻ in its valence shell, it is a highly reactive species as the atomic size of carbon is small and negative charge leads to instability.

Stability is determined by −

• Inductive Effect −  Since, carbanions are electron rich, electron donating alkyl groups will increase the electron density making it unstable. It is thus stabilized inductively by electron withdrawing groups.

• Thus, order of stability of carbanions −

  1⁰ (CH₃CH₂⁻) > 2⁰(CH₃)₂CH⁻ > 3⁰(CH₃)₃C⁻

• Electronegative atoms also stabilizes carbanions inductively by withdrawing the electrons from carbon atom which due to its small size cannot accommodate an extra electron and becomes highly reactive.

• Resonance effect − A negative charge adjacent to π −bonds can disperse its charge through multiple atoms by resonance.

  For example,



• Hybridization − Hybridization with more s −character stabilizes carbanion. s −orbtial lies closer to the nucleus than p. Thus, sp > sp² > sp³