The effect of donation of
electron density from filled π or n
π-orbitals to the symmetry adapted σ*-orbital(s) of σ-bond(s) of a molecular entity resulting in building π-character into bonds that nominally possess only σ-character. The consequences of the effect are, for example, in elongation of the
C–F
bond in the β-fluoroethyl
anion and stabilization of the
anti-
periplanar conformation of fluoromethylamine.
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