Elimination Reaction

Chemists classify reactions into different categories depending on how the atoms are rearranged. The most basic type of reaction is the atom-transfer reaction, which is when two atoms switch places. There are several other types of reactions, including the elimination reaction. In this blog post, we will take a simple look at elimination reactions, types of elimination reactions, elimination reaction mechanisms, and elimination reaction examples.

Meaning of Elimination Reaction:

Elimination reactions are defined as those chemical reactions in which a molecule of a compound splits up into two or more molecules of simpler substances on heating. The process of elimination reactions is the reverse of that of combination or synthesis reactions.

Important Method of Elimination Reaction

The elimination reaction consists of two important methods that include dehydration and dehydrohalogenation.

Dehydration:  The loss of water from the molecule is called dehydration. In this type of elimination, an alcohol or an organic compound containing the -OH group is heated with an inorganic acid like HCl, HBr, or HI. The products formed in this reaction are alkene or alkyne.

Dehydrohalogenation:  The loss of HX from an alkyl halide is called dehydrohalogenation. In this type of elimination, the alkyl halide is heated with a strong base like KOH, NaOH, or Ca(OH)₂. The products formed in this reaction are alkene or alkyne.

Elimination reactions are important because they can be used to synthesise a wide variety of organic compounds. The main advantage of this reaction is that it is a one-step process. This means that the products can be obtained in high yield and with

Types of Elimination Reaction:

There are two types of elimination reaction namely unimolecular and bimolecular.

Unimolecular Elimination Reaction: It is a type of reaction in which only one molecule is involved in the rate-determining step. It is also called E1 reactions.

Bimolecular Elimination Reaction: In a bimolecular elimination reaction, there are two molecules involved in the rate-determining step It is also known as the E2 reaction.

Elimination Reaction Mechanism

There are two types of elimination reactions: E₁ and E₂.

E₁ reactions have the rate-determining step taking place in a single step. It is said to be the two-step for eliminating the process of the formation of carbocation and deprotonation.

E₂ reactions have the rate-determining step taking place in two steps. In the first slow step, the bond between the leaving group and the α-carbon is broken, forming a carbocation. In the second step, nucleophilic attack by the base removes a proton from the β-carbon, causing deprotonation and forming the alkene product.

The mechanism of an E₁ reaction is shown below:

The first step is called the slow, or rate-determining, step. In this step, a bond between the leaving group and the α-carbon is broken, forming a carbocation.

In the second step, nucleophilic attack by the base removes a proton from the β-carbon, causing deprotonation and forming the alkene product.

The mechanism of an E₂ reaction is shown below:

In the first slow step, the bond between the leaving group and the α-carbon is broken, forming a carbocation.

In the second step, nucleophilic attack by the base removes a proton from the β-carbon, causing deprotonation and forming the alkene product.

Elimination reactions are important in organic synthesis because they can be used to synthesise alkenes from alkanes.

For example, the following reaction can be used to synthesise ethene from ethane: 

This reaction is an example of an E₂ elimination reaction.

The reactants are ethane and bromine. The products are ethene and hydrogen bromide.

The mechanism of this reaction is shown below:

In the first slow step, the bond between the bromine and the α-carbon is broken, forming a carbocation.

In the second step, nucleophilic attack by the hydrogen atom removes a proton from the β-carbon, causing deprotonation and forming ethene.

Hydrogen bromide is formed as a by-product of this reaction.

What are the uses of Elimination Reaction?

Elimination reactions can be used for various purposes. It is used to produce alkenes from alkanes. It can also be used to produce dienes from alkynes. Elimination reactions can also be used to produce aromatic compounds.

Conclusion

Elimination reactions are an important class of organic reactions and understanding them is crucial for any student of organic chemistry. Elimination reactions are those reactions in which a bond is broken and two new products are formed. The common types of elimination reactions are E0, Ei, and Eii reactions. The two most common types of elimination reactions are the E1 and E2 mechanisms, each with its own set of reactivity requirements and product characteristics. This article dealt with the types of elimination reactions, elimination reactions mechanism, and elimination reaction examples. With a little practice, students should be able to identify the type of elimination reaction taking place and predict the products formed.