Conformation of n butane | organic chemistry 4th sem | B pharmacy

CONFIRMATION OF n-BUTANE 

In order to understand various confirmation butane it is regarded as a derivative of ethane.

On rotation about C²-C³ sigma bond by 60° each time, we get  staggered and eclipsed conformations of n-butane.

(i) Anti-Conformation :- 

In this conformation, methyl groups and hydrogen linked to two carbon atoms are at a maximum distance apart. It is assumed that the angle of rotation around the C² and C³ bond is zero for this conformation. 

(ii) Eclipsed conformation :-

Starting from the anti conformation, if we rotate the C²- C³ (Sigma) bond through 60°, we get the partially eclipsed form. 

(iii) Gauche or skew conformation :-

On rotating C²- C³ sigma bond by another 60°, we get the staggered conformation also known as gauche or skew from. 

(iv) Fully eclipsed conformation :-

The rotation of C²- C³ sigma bond by another 60° gives rise to fully eclipsed conformation.

Further rotation of 60° gives rise to the Gauche form.It changes to another eclipsed form  on rotating C²- C³ bond by 60° and then to an anti form  by another rotation by 60°.

Various conformation of n-butane and their interconversions are shown below :

Relative stability of conformation of n butane :-

Fully eclipsed < partially eclipsed < Gauche < anti