Question

What is the order of potential energies of the given conformers of 1, 2 - dichloroethane?

• A. I < II < III < IV
• B. IV < III < II < I
• C. II < I < III < IV
• D. II < I < IV < III

Answer 1

The correct option is C II < I < III < IV

Staggered conformations are more stable than eclipsed. Therefore, (I) and (II) are more stable than (III) and (IV).
Since anti (staggered) is more stable conformation than gauche (staggered) due to maximum distance between bulky group (Cl here). Thus, (II) is more stable than (I)
Due to high torsional strain in (IV), it is most unstable.
So order of stability is
II > I > III > IV
Since, stability is inversely proportional to potential energy.
Order of potential energy is
II < I < III < IV