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In organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain ...
, negative hyperconjugation is the donation of electron density
Electron density or electronic density is the measure of the probability of an electron being present at an infinitesimal element of space surrounding any given point. It is a scalar quantity depending upon three spatial variables and is typical ...
from a filled π- or p-orbital to a neighboring σ*-orbital. This phenomenon, a type of resonance
Resonance is a phenomenon that occurs when an object or system is subjected to an external force or vibration whose frequency matches a resonant frequency (or resonance frequency) of the system, defined as a frequency that generates a maximu ...
, can stabilize the molecule or transition state
In chemistry, the transition state of a chemical reaction is a particular configuration along the reaction coordinate. It is defined as the state corresponding to the highest potential energy along this reaction coordinate. It is often marked w ...
. It also causes an elongation of the σ-bond
In chemistry, sigma bonds (σ bonds) or sigma overlap are the strongest type of covalent chemical bond. They are formed by head-on overlapping between atomic orbitals along the internuclear axis. Sigma bonding is most simply defined for diatom ...
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
In organic chemistry, hyperconjugation (σ-conjugation or no-bond resonance) refers to the delocalization of electrons with the participation of bonds of primarily σ-character. Usually, hyperconjugation involves the interaction of the electron ...
(from a σ-orbital to an empty p-orbital).
See also
* Negative hyperconjugation in silicon *Conjugated system
In physical organic chemistry, a conjugated system is a system of connected p-orbitals with delocalized electrons in a molecule, which in general lowers the overall energy of the molecule and increases Chemical stability, stability. It is Reson ...
References
{{Reflist Physical organic chemistry