Negative hyper-conjugation

{
  "id": "MLC-T-CHM-007803",
  "term": "Negative hyper-conjugation",
  "field": "Chemistry",
  "definition": "The donation of electron density from a filled lone-pair or pi orbital into an adjacent empty antibonding sigma orbital, most effectively that of a bond to an electronegative atom such as fluorine. It weakens and lengthens that sigma bond and stabilizes anions, as in the elongated C-F bonds of a beta-fluorocarbanion, in contrast to ordinary hyperconjugation, in which a filled sigma bond is the electron donor.",
  "subject": "Organic and Biomolecular Chemistry",
  "see_also": [
    "anion",
    "anti",
    "conformation",
    "electron density",
    "torsion angle"
  ],
  "references": [
    "PAC, 1999, 71, 1919. 'Glossary of terms used in theoretical organic chemistry' on page 1954 (https://doi.org/10.1351/pac199971101919)"
  ],
  "url": "https://mlchart.com/terminology/chemistry/negative-hyper-conjugation/"
}