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In organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J.; ...
, negative hyperconjugation is the donation of electron density
In quantum chemistry, 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 va ...
from a filled π- or p-orbital to a neighboring σ*-orbital. This phenomenon, a type of resonance
Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillatin ...
, 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 wi ...
. It also causes an elongation of the σ-bond by adding electron density to its antibonding orbital
In chemical bonding theory, an antibonding orbital is a type of molecular orbital that weakens the chemical bond between two atoms and helps to raise the energy of the molecule relative to the separated atoms. Such an orbital has one or more no ...
.
Negative hyperconjugation is seldom observed though its 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 π- or p-orbital to 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 lone pair of electrons to an empty p-orbital).
See also
*Conjugated system
In theoretical 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 stability. It is conventionally represented as ...
References
{{Reflist Physical organic chemistry