Figure 8
According to this system, the conformational isomers of butane due to rotation about the C2-C3 bond may be named as:
Thus, the conformational analysis diagram of the different conformational isomers of n-butane due to rotation about C2-C3 bond as a function of dihedral angle is given below (Figure 10). As expected the synperiplanar conformer having methyl groups eclipsed with each other has the highest energy and is least stable. The other eclipsed conformations have lower energy than the synperiplanar conformer. These are the two anticlinal conformations. The staggered conformers also show a similar pattern. Thus, there are two synclinal conformers (also called gauche conformers) where the two methyl groups are at an angle of 60° to each other. If we consider angle of torsion the then the two anticlinal conformers may be differentiated according to the sense of rotation of the angle of torsion. Thus they may be termed as +anticlinal (P-gauche) for a positive angle of torsion or –anticlinal (M-gauche) for a negative angle of torsion. The anticlinal conformations may also be prefixed with + or – to denote the angle of torsion.