Carbocation rearrangement is one of the most noted chapters of organic chemistry. Many questions related to it are asked in the IIT JEE entrance examination. It is very common in organic chemistry. It is explained as the movement of a carbocation from an unstable condition to a stable condition through the use of different structural reorganizational shifts in the molecules. Once it has moved to a different carbon, it can be said that there is a structural isomer of the molecule.
What is Carbocation rearrangement?
It is a phenomenon that involves reorganization of the structure of a molecule that allows carbocation to become more stable. Thus, a basic carbocation will undergo rearrangement to become tertiary carbocation. Basically, rearrangements involve two adjacent carbons, so they are known as 1-2 rearrangements, whereas a single hydrogen atom or a methyl group moves from carbon next to the carbocation. The displacement of the methyl group is known as ‘alkyl shift’ while the displacement of hydrogen is known as ‘hydride shift’. A carbocation rearrangement is a cause why a reaction gives the blend of various products when there is an expectation of a single product.
All carbocations do not have appropriate hydrogen atoms that are on adjacent carbon atoms for the purpose of rearrangement. Under this condition, the reaction can undergo a different way of rearrangement, chiefly called as alkyl shift. Alkyl shift works quite similar to hydride shift. Instead of shifting of the proton with the nucleophile, an alkyl group is shifted with the nucleophile. This shifting group takes it electron pair with it to build a bond with an adjacent carbocation.
When molecules are attacked by a nucleophile, two products are seen to be formed—a major and minor product. The former is the rearranged product, which is more stable. The latter is the normal product, which is less stable. When it comes to reaction, the formed carbocations undergo rearrangement, which is called as hydride shift. This means that the two electron hydrogen coming from the unimolecular substitution goes over to the neighbouring carbon. One will get to see the phenomenal of hydride shift with the reaction of hydrogen halides and an alcohol.
What is noteworthy about Carbocation rearrangements?
This phenomenon mostly occurs in organic chemistry reactions. But, it is often neglected. According to noted chemists, it can be observed with different analogies.
Carbocation rearrangements for E1 Reactions
E1 reactions are tremendously affected by alkyl shift. The formation of both major and minor products can be seen.
What should students do?
Carbocation rearrangement is a big concept and plays a very important role in organic chemistry. Students need to go through this concept with undivided attention to get complete knowledge about it. They can understand it very well by drawing its structure. Questions related to Carbocation rearrangement will be of the objective type in the JEE entrance exam and students need to be quick-witted to give replies.