The Mystery of Isomerism in Chemistry

by Yuvi K - December 16, 2023

Introduction

Isomerism is one of the most interesting and least understood principles in chemistry. It has been a mystery to many chemists over the centuries and still continues to intrigue scientists today. Isomerism is defined as the phenomenon of different molecules having the same molecular formula with different structures and properties. This phenomenon can occur when two compounds contain the same amount of atoms but differ in the arrangement of those atoms. Isomerism can be divided into four major categories, namely, structural isomerism, stereo isomerism, position isomerism and functional isomerism.

Structural Isomerism (संरचनात्मक इसोमरिज़म)

Structural isomerism occurs when two molecules have the same number and type of atoms but differ in the connection (bond) between them. This is also known as constitutional isomerism (संविधानी इसोमरिज़म). For example, there are two types of structural isomers of pentane C5H12- – n-pentane and isopentane. n-Pentane and Isopentane have the same molecular formula C5H12, i.e., they have 5 Carbon atoms and 12 Hydrogen atoms but the arrangement of those atoms into a particular structure is different.

Stereo Isomerism (स्टीरीय इसोमरिज़म)

Stereo isomerism (also known as optical isomerism or geometrical isomerism) is the type of isomerism where two molecules have the same molecular formula but differ in the stereochemistry of their atoms. Stereochemistry refers to the 3-dimensional arrangement of atoms in a molecule. For example, Lactic Acid (C3H6O3) has two stereo isomers – L- and D- Lactic Acid. L- Lactic acid and D- Lactic acid have the same molecular formula but differ in the arrangement of their atoms.

Position Isomerism (पोज़ीशन इसोमरिज़म)

Position isomerism is the type of isomerism where two molecules have the same molecular formula but differ in the position of their functional groups. Functional groups are specific groups of atoms in a molecule that are responsible for the characteristics of the molecule. For example, alcohols are compounds that contain a hydroxyl group (-OH) as a functional group. The two position isomers of ethanol C2H5OH have the same molecular formula but differ in the position of their -OH group. The first isomer is Methanol (CH3OH) and the other is Ethanol (C2H5OH).

Functional Isomerism ( फ़ंक्शनल इसोमरिज़म)

Functional isomerism is the type of isomerism where two molecules have the same molecular formula but differ in terms of their functional groups. For example, there are two functional isomers of pentane C5H12 – n-pentane and Cyclopentane. n-Pentane and Cyclopentane have the same molecular formula C5H12, i.e., they have 5 Carbon atoms and 12 Hydrogen atoms but the arrangement of those atoms into a particular functional group is different.

Conclusion

Isomerism is an interesting and complex phenomenon in chemistry. It is a type of chemical reaction in which two molecules have the same molecular formula but differ in terms of their structure, stereochemistry, position or functional group. Isomerism is divided into four major categories – structural isomerism, stereo isomerism, position isomerism and functional isomerism. Understanding isomerism is important for chemists since it can help them to predict the properties of compounds and to design new compounds with specific properties.