(a) Do HF/6-31G* partial geometry optimizations of n-butane conformations with CCCC dihedral angles fixed at several values. Plot the energy versus dihedral angle. From the plot, estimate the barriers for the conversions gauche → anti and anti → gauche.
(b) Start from a 60o dihedral angle and do a full geometry optimization to find the predicted dihedral angle for the gauche conformer. Calculate the predicted energy difference between gauche and anti conformers at 0 K, neglecting zero-point energy.