Which of the following biphenyl derivatives exhibits optical activity due to restricted rotation (at — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

For a biphenyl to exhibit optical activity (atropisomerism), two conditions must be met: (1) Steric hindrance from bulky groups at the ortho positions (2, 2', 6, 6') must restrict rotation around the C-C single bond, forcing the rings into perpendicular planes. (2) Each individual ring must be asymmetric relative to the biphenyl axis so that the entire molecule lacks a plane or center of symmetry. Option A has four ortho methyl groups, but since both ortho groups on each ring are identical, a plane of symmetry exists. Options C and D lack sufficient ortho steric hindrance and are planar. Option B has bulky ortho substituents ($-NO_2$ and $-COOH$), forcing a non-planar geometry, and since the ortho groups on each ring are different, it lacks a plane of symmetry, making it optically active.