Question

Equal amounts of (e, e) and (a, a) conformers of trans–1, 2–dichloro cyclohexane exist in non–polar solvents but the (e, e) conformers exists in polar solvents. Explain.

Answer 1

 In (I), there is dipole-dipole repulsion between two equatorial Cl atoms. It partially destabilises the sterically more favoured (e, e) conformer but not the (a, a) conformer (II) where Cl atoms are further apart. Therefore, the conformers (I) and (II) coexist together because their energies are very close. But the polar solvent molecules surround the Cl atoms by dipole – dipole attraction and relieve the dipole-dipole repulsion between Cl atoms themselves. Hence, the lower energy (e, e) conformer (I) predominates in polar solvents.