Negative hyperconjugation

A schematic representation of negative hyperconjugation. In real systems, several of the hydrogens are replaced with other functional groups.

In organic chemistry, negative hyperconjugation is the donation of electron density from a filled π- or p-orbital to a neighboring σ^*-orbital.^[1] This phenomenon, a type of resonance, can stabilize the molecule or transition state.^[2] It also causes an elongation of the σ-bond by adding electron density to its antibonding orbital.^[1]

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.^[3]^[4]

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).

References

^ ^a ^b "Negative Hyper-Conjugation" (PDF). Old.iupac.org. Archived from the original (PDF) on 2012-03-24. Retrieved 2013-10-23.
^ "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.
^ "Negative hyperconjugation of some fluorine containing groups – New Journal of Chemistry (RSC Publishing)". Pubs.rsc.org. Retrieved 2012-08-20.
^ 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.

Zdroj:https://en.wikipedia.org?pojem=Negative_hyperconjugation
Text je dostupný za podmienok Creative Commons Attribution/Share-Alike License 3.0 Unported; prípadne za ďalších podmienok. Podrobnejšie informácie nájdete na stránke Podmienky použitia.

[iupac1-1] "Negative Hyper-Conjugation" (PDF). Old.iupac.org. Archived from the original (PDF) on 2012-03-24. Retrieved 2013-10-23.

[2] "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.

[3] "Negative hyperconjugation of some fluorine containing groups – New Journal of Chemistry (RSC Publishing)". Pubs.rsc.org. Retrieved 2012-08-20.

[4] 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.

[1]

[2]

[3]

[4]

See also

References