Class 11 Chemistry Hydrocarbons Conformational Isomerism

Conformational Isomerism

It arises due to free rotation around C – C bond. We can define it as:

Definition: The different arrangement of atoms in space which can be obtained due to rotation about

C – C bond are called Conformation. It is not totally free but there is energy barrier of 120kJ/mol that has to be overcome.  This is called torsion strain that exist between two forms.

Conformations of ethane: There are two projections.

  •  Sawhorse projection: In this H and C are bonded to each other and is represented in form of lines.



  •  Newman projection: In this carbon is represented by drawing circles and hydrogen are represented by drawing lines as shown.



The two form of new man projection are: eclipsed and staggered

  • Staggered: In this hydrogen are far apart from each other


  • Eclipsed: this hydrogen are just at back of each other



When staggered is rotated by 600 we get eclipsed form .In this: 600 -torsional angle .Torsional angle is angle by which one form is rotated to get the other form.

Torsional strain: It is the repulsive force that acts and give differnt stability of different forms .


The difference in their energy is given above and this is easily overcome and they keep inter converting.

In this cyclohexane: We have two forms that are shown:



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