What is the Difference Between Chain Isomerism and Position Isomerism

The key difference between chain isomerism and position isomerism is that chain isomerism describes the occurrence of different main carbon chains in two compounds with the same chemical formula, whereas position isomerism is the occurrence of a similar carbon skeleton and functional group, but the functional groups are attached to the main carbon chain in different positions.

Isomerism describes the property of some molecules in which more than one compounds have the same chemical formula but different chemical structures.

CONTENTS

1. Overview and Key Difference
2. What is Chain Isomerism
3. What is Position Isomerism
4. Chain Isomerism vs Position Isomerism in Tabular Form
5. Summary – Chain Isomerism vs Position Isomerism

What is Chain Isomerism?

Chain isomerism is the difference in the arrangement of carbon chains with the molecule. We can describe it by comparing two compounds with the same molecular formula having a different main carbon chain. In other words, the carbon atoms in the main chain of the isomers are joined together in a different way.

In this type of isomerism, the carbon chain can be straight or branched. A simple example of this type of isomer is the chemical compound having the chemical formula C5H12. It has three major chain isomers: n-pentane, 2-methylbutane and 2,2-dimethylpropane.

What is Position Isomerism?

Position isomerism is the presence of a similar carbon skeleton and functional groups in two or more organic compounds when the location of the functional groups is different from each other. The number of carbon atoms, molecular formula, carbon backbone structure, and the number of functional groups are the same for the isomers in position isomerism. This type of isomerism is absent in compounds having end groups like carboxylic acids and aldehydes since these groups cannot be positioned in the middle of a carbon chain.

Let us consider an example to understand this type of isomerism. The alcoholic compounds for the chemical formula C5H12O can be written in three main ways depending on the position of the –OH group. Here, the –OH group can be positioned in the terminal of the molecule, in the middle of the molecule, or on the 2nd carbon atom from one terminal.

Position isomerism can be observed in alkene and alkynes as well. Here, the position of the double bond or the triple bond is different from one molecule to another. But in carboxylic acids, amides, and aldehydes, position isomerism is absent because these functional groups are essentially located only in the terminals of the molecule.

What is the Difference Between Chain Isomerism and Position Isomerism?

Isomerism describes the property of some molecules in which more than one compounds have the same chemical formula but different chemical structures. The key difference between chain isomerism and position isomerism is that chain isomerism describes the occurrence of different main carbon chains in two compounds with the same chemical formula, whereas position isomerism is the occurrence of a similar carbon skeleton and functional group, but the functional groups are attached to the main carbon chain in different positions.

The following table summarizes the difference between chain isomerism and position isomerism.

Summary – Chain Isomerism vs Position Isomerism

The key difference between chain isomerism and position isomerism is that chain isomerism describes the occurrence of difference main carbon chains in two compounds with the same chemical formula whereas position isomerism is the occurrence of a similar carbon skeleton and functional group but the functional groups are attached to the main carbon chain in different positions.

Reference:

1. “Isomerism – Definition, Detailed Explanation, Types, Examples.” BYJU’S, 28 May 2021.

Image Courtesy:

1. “Alkane structure 3” By 1840460mahesh – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Isomeren” By Rob Hooft at Dutch Wikipedia (CC BY-SA 3.0) via Commons Wikimedia