negative hyper-conjugation
The effect of donation of @[email protected] from filled π or nπ-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 @[email protected] and stabilization of the @[email protected]@[email protected] @[email protected] of fluoromethylamine.
PAC, 1999, 71, 1919. (Glossary of terms used in theoretical organic chemistry) on page 1954 [Terms] [Paper]