1Steric strain is (i.e., the extra energy) put on a molecule when atoms or
groups are too close to one another, which results in repulsion between the electron
clouds of these atoms or groups. For example, there is more steric strain in a gauche
conformer than in the anti conformer because the two methyl groups are closer together
in a gauche conformer. This type of steric strain is called a gauche interaction.
hence due to steric interaction of the methyl groups the dihedral angle beetween the methyl groups in the gauche conformation of n-butane is actually somewhat larger than 60° .
