Isomerism Definition, types Explained.

The concept of Isomerism is important feature of Organic Compounds. There are more than 10 million organic compounds are present, many of which exhibit Isomerism property, which enhances the diversity of Organic compounds. In this topic you will learn all basics of isomerism in detail. Both A Level as well as O Level students can use this content for their preparation as reference.


“Two or more compounds having the same molecular formula but different structural formula and properties are said to be isomersĀ  and the phenomenon is called isomerism.”


If we study the structural formula of butane or higher hydrocarbons of Alkane family, we will observe that it is possible to arrange the atoms present in the molecule in more than one way to satisfy all valencies. For example, butane molecule can have two different arrangements as represented by the following structural formula.

This fact have been supported by an experimental evidence that there are two compounds with different physical properties but with the same molecular formula of C4H10.

Which Organic Compounds do not show isomerism?

The alkanes, methane, ethane and propane do not show phenomenon of isomerism because each exist in one structural form only.

The five carbon compound, pentane has three isomerism.When the number of carbon atoms increases to thirty, the number of isomers amount to over four billions.

Types of Structural Isomerism

All classes of organic compounds and their derivatives show the phenomenon of structural isomerism. The structural isomerism arises due to difference in the arrangement of atoms within the molecule.

The structural isomerism can be exhibited in five different ways. These are:

  1. The chain Isomerism
  2. Position Isomerism
  3. Functional group Isomerism
  4. Metamerism
  5. Tautomerism

The Chain Isomerism

This type of isomerism arises due to the difference in nature of carbon chain. For example: for pentane (C5H12).

The following arrangements are possible:

Position Isomerism

This type of isomerism arises due to difference in the position of the same functional group on the carbon chain. The arrangement of carbon atoms remains the same.

For Example:

Functional Group Isomerism

The compounds having the same molecular formula but different functional groups are said to exhibit functional group isomerism.

For example, there are two compounds having same molecular formula C2H6O, but different arrangement of atoms.


Isomerism arises due to the unequal distribution of carbon atoms on either side of the functional group.

For example: Diethyl ether and methyl-n-propyl ether are metamers.

For a ketonic compound having the molecular formula C5H10O. The following two metamers are possible.


This type of isomerism arises due to shifting of proton from one atom to other in the same molecule.



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Fawad's Chemistry

Hope you fine. I'm Fawad and author of this blog "Chemanalogy". Love to write on Chemistry. Currently teaching A Levels, O Levels and University Chemistry offline as well as online. Connect to chemanalogy community by subscribing via email.