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 seldom observed, though it can be most commonly observed when the σ*-orbital is located on certain C–F or C–O bonds.
In negative hyperconjugation, the electron density flows in the opposite direction (from a π- or p-orbital to an empty σ*-orbital) than it does in the more common hyperconjugation (from a σ-orbital to an empty p-orbital).
See also
References
"Negative Hyper-Conjugation" (PDF). Old.iupac.org. Archived from the original (PDF) on 2012-03-24. Retrieved 2013-10-23. https://web.archive.org/web/20120324085532/http://old.iupac.org/goldbook/NT07081.pdf ↩
"2.2.3 Negative Hyperconjugation for Ebooksclub.org Molecular Orbitals and Organic Chemical Reactions Student Edition". Scribd.com. 2011-04-29. Retrieved 2012-08-20. https://www.scribd.com/doc/54173058/46/Negative-Hyperconjugation ↩
"Negative Hyper-Conjugation" (PDF). Old.iupac.org. Archived from the original (PDF) on 2012-03-24. Retrieved 2013-10-23. https://web.archive.org/web/20120324085532/http://old.iupac.org/goldbook/NT07081.pdf ↩
"Negative hyperconjugation of some fluorine containing groups – New Journal of Chemistry (RSC Publishing)". Pubs.rsc.org. Retrieved 2012-08-20. http://pubs.rsc.org/en/content/articlelanding/2008/NJ/b718430a ↩
Karni, Miriam; Bernasconi, Claude F.; Rappoport, Zvi (2007-08-09). "Role of Negative Hyperconjugation and Anomeric Effects in the Stabilization of the Intermediate in SNV Reactions". The Journal of Organic Chemistry. 73 (8): 2980–2994. doi:10.1021/jo7017476. PMID 18376875. /wiki/Doi_(identifier) ↩