The illustration of butane above is represented by the newmann projection below by designating the two middle carbons, one as the "front" and one as the "behind" carbon, and connecting the two end methyl groups accordingly.
In the most stable conformation, the two methyl groups lie as far apart from each other as possible with a dihedral angle of 180 degrees. This particular staggered conformation is called anti. The other staggered conformation has a Me-Me dihedral angle of 60 degrees and is called gauche. The gauche form is less stable than the anti form by 0.9 kcal/mol due to steric hindrance between the two methyl groups. Such an interaction is often referred to as a gauche-butane interaction because butane is the first alkane discovered to exhibit such an effect.
The conformations of butane are fully clipsed ( angle 0 or 360), gauche ( angle 60 or 300) , eclipsed ( angle 120or 240), and anti ( angle 180).Fully eclipsed is least stable about 18.4-25.5 kJ/mol than anti conformation. . gauche conformations are about 3.35 kJ/mol less stable than anti conformation.The eclipsed conformation is less stable than gauche by about 10.85 kJ/mol and than anti conformation by about 14.2 kJ/mol.
The diagramatic representation has already appeared.