Class 11 Chemistry Organic Chemistry Isomerism


It is existence of compounds in two or more forms, having same molecular formula but different physical and chemical properties.

It is basically of two types:

  • Structural
  • Stereoisomerism

Structural isomerism: Differ in arrangement            of atoms within molecule.         

Stereoisomerism: Differ in arrangement of atom in space.

The structural isomerism type:

  • Chain
  • Position
  • Functional
  • Meta-merism
  • Tauto-merism

The different types of stereoisomerism are:

  • Geometrical
  • Optical
  • conformational

Let us study first structural isomerism types :

  1. Chain isomerism– The compounds that have same molecular formula ,but different arrangement of atoms within the chain.


  1. Position isomerism: The compounds with same molecular formula, but differ in position of substituent, side chain or functional groups.


  1. Functional isomerism: The compounds with same molecular formula but differ in type of functional group and also in physical and chemical properties.


  1. Metamerism: The compounds that have same molecular formula ,but differ in number of carbon atoms around functional group.

 It is shown by functional groups like ether, esters, ketones.



  1. Tautomerism: In this simultaneous movement of π electron cloud and Hydrogen take place. Most common tautomerism is keto – enol tautomerism.


let us study stereo isomerism now   

In it the compounds have same molecular formula , but different arrangement of atoms in three-dimensional space.

It is of three types:

  1. Geometrical : It arises due to restricted rotation around C=C bond.

Conditions required are :

  1. Presence of C=C bond.
  2. The two groups attached to carbon atoms must be different.






  • As far as stability is concerned, more bulky is the group, more is the Stearic hindrance.
  • Stearic hindrance which creates obstruction in rotation therefore, less is the stability.

      But-2-ene> Pent-2-ene-Hex>3-ene                 

CONFORMATIONAL ISOMERISM: It exists in Alkanes (C-C). It is due to full rotation around C-C single bond.

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