Question

The Dihedral Angle Between Two Methyl Groups In Partially Eclipsed Conformation Of N-Butane Is _______

Answer 1

When the dihedral angle = 0° or 360°, (syn conformation) in butane, the two methyl groups are in close proximity with the molecule, therefore the potential energy is at its highest.

When the dihedral angle = 60° or 300°, (gauche conformation) in butane, the methyl groups are farther apart and therefore the potential energy drops by 4.1 kcal/mol.

When the dihedral angle = 120° or 240°, (eclipsed conformation) in butane, the methyl groups align themselves with hydrogens on the same plane, resulting in the butane having a higher potential energy than the gauche conformations though still having a lower potential energy than the syn conformation ( dihedral angle = 0° or 360°) by 1.5 kcal/mol.