Electrophilic Substitution Reaction Mechanism in Organic Chemistry

by Yuvi K - December 17, 2023

Electrophilic Substitution Reaction Mechanism in Organic Chemistry: A Detailed Overview

Organic chemistry is one of the most important branches of chemistry, as it deals with the study of compounds which are based on carbon atoms. In organic chemistry, one of the most important and popular reactions is the Electrophilic Substitution Reaction, commonly known as ESR. The Electrophilic Substitution Reaction mechanism involves the replacement of a hydrogen atom in an organic molecule by an electrophile molecule.

What is an Electrophile?

An electrophile is a molecule which has a partial positive charge on one of it’s atoms. This partial positive charge is attracted to the electron rich substitutes of the carbon atom. To explain this concept in a better way, let us take an example of an acetate molecule. On breaking the acetate, we get one acetate ion and one chlorine atom. Now, the chlorine atom is partially positively charged, so it is attracted to the electron rich carbon atom, which forms a new bond. This situation is an example of an electrophile.

What is a Selectrophilic Substitution?

Electrophilic Substitution Reacttion or ESR is an organic chemistry reaction which involves the replacement of a hydrogen atom present in an organic molecule.The molecule which replaces the hydrogen atom in the organic molecule is termed as an electrophile. The reaction mechanism of Electrophilic Substitution Reaction involves three steps- Ionization, Attack and Protonation.

Stepwise Mechanism of Electrophilic Substitution Reaction:

Association:

In the first step of Electrophilic Substitution Reaction, the electrophile molecule is associated with the organic molecule. This association is so strong that the electrophile molecule breaks the bond of the hydrogen atom with the organic molecule and forms a new bond with it.

Attack:

In the second step of the ESR mechanism, the electrophile molecule attacks the organic molecule. This process involves the electrostatic attraction of the partially positively charged atom of the electrophile molecule and the electron-rich substrate of the organic molecule. This results in the breakage of the bond of the hydrogen atom with the organic molecule and the formation of a new bond between the electrophile and the organic molecules.

Protonation:

The final step of the mechanism involved is protonation. In this process, the proton present on the electrophile molecule is attracted towards the negative charge present on the organic molecule. As a result, a new bond is formed between the proton and the organic molecule.

Types of Electrophilic Substitution Reaction:

Electrophilic Substitution Reaction can be further classified into two types-

• SN1 (Substitution Nitrogenous 1) : SN1 stands for Substitution Nitrogenous 1. This reaction involves a single-step mechanism, in which the electrophile attaches itself to the organic molecule and forms a bond with it.
• SN2 (Substitution Nitrogenous 2) : This type of Electrophilic Substitution Reaction is a two step process, wherein the first step involves the preparation of a carbocation, and the second step involves the formation of a new bond between the proton and the organic molecule.

Examples Of Electrophilic Substitution Reaction:

The most common example of Electrophilic Substitution Reaction involves the reaction between chlorine and ethane. In this reaction, the chlorine atom (acting as the electrophile) forms a covalent bond with the carbon atom of ethane by replacing the hydrogen atom present in ethane.

Another example of Electrophilic Substitution Reaction involves the reaction between bromine and ethane. In this reaction, the bromine atom (acting as the electrophile) forms a covalent bond with the carbon atom of ethane by replacing the hydrogen atom present in ethane.

Advantages of Electrophilic Substitution Reaction:

• The reaction is relatively easy to perform and can be used to produce different types of compounds in a single step.
• The products which are obtained by performing Electrophilic Substitution Reactions exhibit certain specific properties which make them ideal for a variety of applications.
• Electrophilic Substitution Reactions are comparatively cost-effective and low in toxicity, making them suitable for use in a wide range of industries.
• The products which are obtained from Electrophilic Substitution Reactions are often of higher purity than their starting materials, which makes them ideal for a wide range of applications.

Conclusion

To sum up, Electrophilic Substitution Reaction is an important and popular organic chemical reaction. It involves the replacement of a hydrogen atom in an organic molecule by an electrophile molecule. The mechanism involves three steps- association, attack and protonation. The reaction can also be classified into two types – SN1 and SN2. The products obtained via Electrophilic Substitution Reaction can be used for an extensive range of applications in industrial and pharmaceutical industries.

References:

1. Fink, D. L., & Silverman, A. (n.d.). Electrophilic Substitution Reactions. Retrieved April 20, 2021, from https://www.chem1.com/acad/webtext/chembio/electroph.html.
2. Editor, B. S. (2019, April 13). Electrophilic Substitution Reactions. Retrieved April 20, 2021, from https://biologydictionary.net/electrophilic-substitution-reactions/.
3. Sciencing_Contributor. (2017, August 14). Advantage & Disadvantage of Electrophilic Substitution Reactions. Retrieved April 20, 2021, from https://sciencing.com/advantage-disadvantage-electrophilic-substitution-reactions-8367090.html.