why carbanion shows sp3 hybridisation when it is non-conjugated?
why carbanion shows sp2 hybridisation when it is conjugated?
Carbanions are trivalent with sp3 hybridization. The lone pare of electrons occupies one of the sp3 orbitals. The geometery is thus tetrahedral. The tetrahedron can undergo inversion or retain its stereochemistry depending on the attached substitutents. A methyl carbanion has a barrier to inversion of about 2 kcal/ mole. The trifluoromethyl carbanion has a barrier of 120 kcal/mole. A fluorine atom is however more stabilizing than a hydrogen atom because of the fluorine electronegativity. Carbanion have sp2 hybridisation when attached to conjugative groups like olefine, ketone.