The dihedral angle between the two methyl groups of butane (viewed along C2-C3) is varied. Using H/H eclipsing 4.0, H/$\mathrm{CH}{}_3$ eclipsing 6.0 and $\mathrm{CH}{}_3$/$\mathrm{CH}{}_3$ eclipsing 11.0 kJ/mol, gauche 3.8 kJ/mol above anti, select the correct statements.

1. AAt a dihedral angle of $120^{\circ }$ the energy is a local maximum at 16.0 kJ/mol above anti
2. BAt $0^{\circ }$ the energy is the global maximum, 19.0 kJ/mol above anti
3. CThe gauche conformer ($60^{\circ }$) is a local minimum 3.8 kJ/mol above anti
4. DThe barrier for gauche to gauche conversion through the $0^{\circ }$ conformer is 19.0 kJ/mol