Among the conformers, the least stable is the first eclipsed structure, where
two CH3 groups are totally eclipsed, and the most stable is the first staggered
conformer, where two CH3 groups are staggered, and far apart from each
other. When two bulky groups are staggered we get the anti conformation,
and when they are at 60 to each other, we have the gauche conformer. In
butane, the torsional energy is even higher than in propane. Thus, there is
slightly restricted rotation about the C2–C3 bond in butane. The order of
stability (from the highest to the lowest) among the following conformers is
anti! gauche!another eclipsed!eclipsed. The most stable conformer
has the lowest steric strain and torsional strain