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Si–O–C groups are intermediate, tending to have bond angles smaller than Si–O–Si but larger than C–O–C. The main reasons are hyperconjugation (donation from an oxygen p orbital to an Si–R σ* sigma antibonding molecular orbital, for example) and ionic effects (such as electrostatic repulsion between the two neighbouring partially ...
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.
In vinyl cations, there is a marked decrease in the C-R and C=C bond lengths, indicative of electron donation or induction between C a and R, and C b and C a. On the other hand, the increase in the C b -H bond length implies a strong hyperconjugative effect that is inversely related to the thermodynamic stability of the cation.
In chemistry, π backbonding is a π-bonding interaction between a filled (or half filled) orbital of a transition metal atom and a vacant orbital on an adjacent ion or molecule. [ 1 ] [ 2 ] In this type of interaction, electrons from the metal are used to bond to the ligand , which dissipates excess negative charge and stabilizes the metal.
The stereoelectronic effect affecting the outcome of the facial selectivity of the diene in the Diels–Alder reaction is the interaction between the σ(C(sp 2)–CH 3) (when σ(C(sp 2)–X) is a better acceptor than a donor) or σ(C(sp 2)–X) (when σ(C(sp 2)–X) is a better donor than an acceptor) and the σ* orbital of the forming bond ...
In contrast, the C−O−C bond angle in the carbon analogue of disiloxane, dimethyl ether, is 111°. [4] The unusual bond angle in disiloxane has been attributed primarily to negative hyperconjugation between oxygen p orbitals and silicon–carbon σ* antibonding orbitals, p(O) → σ*(Si−R), a form of π backbonding.
In 1935 Baker and Nathan explained the observed difference in terms of a conjugation effect and in later years after the advent of hyperconjugation (1939) as its predecessor. A fundamental problem with the effect is that differences in the observed order are relatively small and therefore difficult to measure accurately.
Figure 9: The C–H bonding orbital is mixing with the C–X anti-bonding orbital through hyperconjugation. Figure 10: In an E 2 mechanism molecules generally prefer an anti-periplanar geometry because it aligns molecular orbitals and sets up the molecule to move electrons in a C–H bonding orbital into a π C-C bonding orbital.