"Exploration of How migration of Hydrogen and migration of Carbon occurs in Sigmatropic Reaction"

"Exploration of How migration of Hydrogen and migration of Carbon occurs in Sigmatropic Reaction"

Migration of Hydrogen:

The s orbital of hydrogen is partially bound to both the migration origin and the migration endpoint in the transition state when a hydrogen migrates in a sigmatropic rearrangement. As a result, a four-membered ring transition state is involved in a [1, 3] sigmatropic migration of hydrogen. The HOMO is asymmetric because it involves two pairs of electrons. Therefore, according to the selection rules, a [1, 3]-hydrogen shift under thermal conditions requires an antarafacial rearrangement. Because the four-membered ring transition state does not permit the necessary antarafacial rearrangement, [1, 3]-hydrogen shifts do not take place under thermal conditions.

[1, 3]-hydrogen shift:

If the reaction is conducted under photochemical conditions, [1, 3]-Hydrogen shifts may occur because the HOMO is symmetric under these circumstances, allowing hydrogen to migrate via a suprafacial channel.

Due to the fact that two distinct allylic hydrogens can go through a 1,3-hydrogen shift, the reaction yields two products.

[1, 5]-hydrogen shift:

[1,5] Hydrogen sigmatropic migrations are well recognised. They take place through a suprafacial pathway under hot conditions because they involve three pairs of electrons.

[1, 7]-hydrogen shift:

In [1,7] sigmatropic hydrogen migrations, four pairs of electrons are involved. They are possible because the eight-membered ring transition state permits the necessary antarafacial rearrangement in thermal conditions.

Migration of Carbons:

Carbon has two routes to migrate because of its two-lobed p orbital, in contrast to hydrogen, which can only migrate in one direction due to its spherical s orbital. Using one of its lobes, carbon can communicate with both the migration's origin and terminus.

If a suprafacial rearrangement is necessary for the reaction, carbon will migrate utilising either one of its lobes if the HOMO is symmetric or both of its lobes if the HOMO is asymmetric.

The migrating group maintains its configuration when carbon migrates with only one of its p lobes engaging with the migration source and migration terminus since bonding is always to the same lobe. Different lobes are involved in bonding in the reactant and in bonding in the product when carbon migrates with both of its p lobes engaging.

The following [1, 3] sigmatropic rearrangement has a four-membered-ring transition state that requires a suprafacial pathway. The reacting system has two pairs of
electrons, so its HOMO is asymmetric. Therefore, the migrating carbon interacts with
the migration source and the migration terminus using both of its lobes, so it undergoes inversion of configuration.