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The reaction process can be shown using two different geometries, the small molecule can approach in a linear or non-linear fashion. In the linear approach, the electrons in the orbital of the small molecule are pointed directly at the π-system. In the non-linear approach, the orbital approaches at a skew angle.
The sp 2 lone pair acts as an electron donor, whereas the empty p-orbital is capable as acting as an electron acceptor. In this example, the β-carbon of the α,β-unsaturated ester 1 formally acts as a nucleophile, [ 4 ] whereas normally it would be expected to be a Michael acceptor .
Orbital overlaps in types I, II and III 1,3-dipolar cycloaddition. 1,3-Dipolar cycloadditions are pericyclic reactions, which obey the Dewar-Zimmerman rules and the Woodward–Hoffmann rules . In the Dewar-Zimmerman treatment, the reaction proceeds through a 5-center, zero-node, 6-electron Huckel transition state for this particular molecular ...
According to the frontier molecular orbital theory, the sigma bond in the ring will open in such a way that the resulting p-orbitals will have the same symmetry as the HOMO of the product. [4] For the 5,6-dimethylcyclohexa-1,3-diene, only a disrotatory mode would result in p-orbitals having the same symmetry as the HOMO of hexatriene.
Molecular orbital diagram of dinitrogen. With nitrogen, we see the two molecular orbitals mixing and the energy repulsion. This is the reasoning for the rearrangement from a more familiar diagram. The σ from the 2p is more non-bonding due to mixing, and same with the 2s σ. This also causes a large jump in energy in the 2p σ* orbital.
In organic chemistry, a rearrangement reaction is a broad class of organic reactions where the carbon skeleton of a molecule is rearranged to give a structural isomer of the original molecule. [1] Often a substituent moves from one atom to another atom in the same molecule, hence these reactions are usually intramolecular.
A cycloaddition is a reaction that simultaneously forms at least two new bonds, and in doing so, converts two or more open-chain molecules into rings. [3] The transition states for these reactions typically involve the electrons of the molecules moving in continuous rings, making it a pericyclic reaction.
In the Bamberger rearrangement N-phenylhydroxylamines rearrange to 4-aminophenols. The nucleophile is water. The Smiles rearrangement is the intramolecular version of this reaction type. Nucleophilic aromatic substitution is not limited to arenes, however; the reaction takes place even more readily with heteroarenes.