A natural bond orbital analysis of carbanions

► Hyperconjugation energies of alkyl carbanions respond to unsymmetrical p-orbital lobes. ► Hybridization indices of p-orbitals show dependency on anionic planarity. ► Hyperconjugation energies correlate with extent of anionic p-character. ► Orientation of p-orbital and CC* bond axes are important factors in hyperconjugation. ► Allylic anions show lower delocalization effects than expected.