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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 ...
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 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.
Stabilization is possible because of a good overlap between the C-H bond and the empty p-orbital at C a. Hyperconjugation is evident in all structures because of the adjacent C b-H bond and in the –CH 3 substituent. Enthalpy calculations obtained from the isodesmic reaction are fair accurate and shows good correlation with experimental data.
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.
Free-radical intermediate is stabilized by hyperconjugation; adjacent occupied sigma C–H orbitals donate into the electron-deficient radical orbital. A new method of anti-Markovnikov addition has been described by Hamilton and Nicewicz, who utilize aromatic molecules and light energy from a low-energy diode to turn the alkene into a cation ...
The Cieplak effect relies on the stabilizing interaction of mixing full and empty orbitals to delocalize electrons, known as hyperconjugation. [2] When the highest occupied molecular orbital of one system and the lowest unoccupied molecular orbital of another system have comparable energies and spatial overlap, the electrons can delocalize and sink into a lower energy level.
The energy difference between gauche and anti is 0.9 kcal/mol associated with the strain energy of the gauche conformer. The anti conformer is, therefore, the most stable (≈ 0 kcal/mol). The three eclipsed conformations with dihedral angles of 0°, 120°, and 240° are transition states between conformers. [6]