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Hyperconjugation can be used to rationalize a variety of chemical phenomena, including the anomeric effect, the gauche effect, the rotational barrier of ethane, the beta-silicon effect, the vibrational frequency of exocyclic carbonyl groups, and the relative stability of substituted carbocations and substituted carbon centred radicals, and the thermodynamic Zaitsev's rule for alkene stability.
Negative hyperconjugation is a theorized phenomenon in organosilicon compounds, in which hyperconjugation stabilizes or destabilizes certain accumulations of positive charge. The phenomenon explains corresponding peculiarities in the stereochemistry and rate of hydrolysis .
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 ...
Small hydride sources, however, add hydride to an axial position for reasons which are still disputed. [3] The Cieplak effect explains this phenomenon by postulating that hyperconjugation of the forming σ* C–H orbital with geometrically aligned σ orbitals is the stabilizing interaction that controls stereoselectivity.
Hyperconjugation model for explaining the gauche effect in 1,2-difluoroethane. Key in the bent bond explanation of the gauche effect in difluoroethane is the increased p orbital character of both C−F bonds due to the large electronegativity of fluorine. As a result, electron density builds up above and below to the left and right of the ...
Furthermore, similar to a positive charged species, the radical species is most stable when the unpaired electron is in the more substituted position. The radical intermediate is stabilized by hyperconjugation. In the more substituted position, more carbon-hydrogen bonds are aligned with the radical's electron deficient molecular orbital.
The carbon-silicon bond is highly electron-releasing and can stabilize a positive charge in the β position through hyperconjugation.Electrophilic additions to allyl- and vinylsilanes take advantage of this, and site selectivity generally reflects this property—electrophiles become bound to the carbon γ to the silyl group.
Hyperconjugation can be used to explain phenomena such as the gauche effect and anomeric effect. Orbital symmetry is important when dealing with orbitals that contain directional components like p and d. An example of such an effect is square planar low-spin d 8 transition metal complexes. These complexes exist as square planar complexes due to ...