ⓘ Negative hyperconjugation. In organic chemistry, negative hyperconjugation is the donation of electron density from a filled π- or p-orbital to a neighboring σ ..

                                     

ⓘ Negative hyperconjugation

In organic chemistry, negative hyperconjugation is the donation of electron density from a filled π- or p-orbital to a neighboring σ * -orbital. This phenomenon, a type of resonance, can stabilize the molecule or transition state. It also causes an elongation of the σ-bond by adding electron density to its antibonding orbital.

Negative hyperconjugation is most commonly observed when the σ * -orbital is located on certain C–F or C–O bonds, and does not occur to an appreciable extent with normal C–H bonds.

In negative hyperconjugation, the electron density flows in the opposite direction from π- or p-orbital to empty σ * -orbital than it does in the more common hyperconjugation from σ-orbital to empty p-orbital.