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