Question

Conformational isomerism can be exhibited by which of the following compounds?

• A. Methane at room temperature
• B. Cyclohexane at /(-100^oC/)
• C. Ethane at room temperature
• D. Benzene at /(100^oC/)

Answer 1

Answer: (A), (C)

The correct options are
A Methane at room temperature
C Ethane at room temperature

Conformational isomerism arises because of the freedom of rotation about carbon-carbon single bonds. These rotations are sometimes hindered by some rotational energy barriers created by torsional or angular strains.

To exhibit conformational isomerism a molecule needs to have:

1. A single bond which allows for free rotation about its axis
2. Enough energy to overcome the rotational energy barrier

Cyclohexane can exhibit conformational isomerism when enough energy is available but at /(-100^oC/) enough energy is not available from the surroundings to overcome the energy barrier.
Benzene has only /(sp^2/) hybridised carbons and double bonds which do not allow for free rotation and so no conformers.