The anti conformation of 1,2-dichloroethane, Cl—CH₂—CH₂—Cl, is 4.81 kJ mol–1 (1.15 kcal mol^–1) more stable than the gauche conformation. The two energy barriers (measured relative to the energy of the gauche conformation) for carbon–carbon bond rotation are 21.5 kJ mol–1 (5.15 kcal mol^–1) and 38.9 kJ mol^–1 (9.3 kcal mol^–1).

(a) Sketch a graph of potential energy versus dihedral angle about the carbon–carbon bond. Show the energy differences on your graph and label each minimum and maximum with the appropriate conformation of 1,2-dichloroethane.

(b) Which conformation of this compound is present in greatest amount? Explain.