In butane, take these eclipsing increments: H/H = 4.0, CH${}_3$/H = 6.0, CH${}_3$/CH${}_3$ = 11 (all kJ/mol), and gauche CH${}_3$/CH${}_3$ = 3.8 kJ/mol. A Newman projection along C2-C3 (C2 in front) shows front groups CH${}_3$ at 12, H at 4, H at 8 o'clock. Starting from the anti conformer (back CH${}_3$ at 6, H at 2, H at 10), the back carbon is rotated 60${}^{\circ }$ clockwise. What is the energy of the resulting conformer relative to anti?

1. A$16.0\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$
2. B$19.0\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$
3. C$12.0\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$
4. D$3.8\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$