hyperconjugation


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hyperconjugation

[‚hī·pər‚kän·jə′gā·shən]
(physical chemistry)
An arrangement of bonds in a molecule that is similar to conjugation in its formulation and manifestations, but the effects are weaker; it occurs when a CH2 or CH3 group (or in general, an AR2 or AR3 group where A may be any polyvalent atom and R any atom or radical) is adjacent to a multiple bond or to a group containing an atom with a lone π-electron, π-electron pair or quartet, or π-electron vacancy; it can be sacrificial (relatively weak) or isovalent (stronger).
References in periodicals archive ?
NBO calculations revealed that the strong intramolecular hyperconjugation interactions, delocalization and intramolecular charge transfer cause the stability of the molecule.
Weinhold, "Electronic basis of improper hydrogen bonding: a subtle balance of hyperconjugation and rehybridization," Journal of the American Chemical Society, vol.
Porter, "Role of hyperconjugation in determining carbon-oxygen bond dissociation enthalpies in alkylperoxyl radicals," Organic Letters, vol.
Hyperconjugation, characteristic infrared absorption of methylsulfones and crystal structures of selected aromaticsulfones.
This led to a model called negative hyperconjugation that was based on p oxygen orbitals interacting with silicon sigma antibonding orbitals.
Hyperconjugation effects on RDX conformation were evaluated because of the lone pair of electrons on the atrazine ring nitrogens.
This would donate a charge through hyperconjugation and by the inductive effect, thus concentrating the charge density on nitrogen and sulfur atoms--thereby increasing their adsorption at the anodic sites of the metal.
It was found that the mesomeric and the hyperconjugation effects have a strong influence on the antibacterial activity.
This might come from the hyperconjugation effect which created by the methyl group of the 3-methylbenzene substituent Scheme 3.
This result is consistent with the concept that the stabilization of aliphatic and alicyclic carbanions is largely dependent on anionic hyperconjugation, involving the interaction between the electronic "lone pair" and antibonding C-H and C-C [[sigma].sup.*] orbitals [beta] to the anionic centre [20-24].
Then, Pophristic looked at the other known influence on ethane's twisting--a quantum mechanical effect known as hyperconjugation. "The electrons of one methyl group jump over to the other methyl group," says Goodman.
They have been using spin density calculations in free radicals to show hyperconjugation and resonance phenomena.