Which of the following biphenyls is optically active?

40 2016 Organic Chemistry - Some Basic Principles and TechniquesStereoisomerism – atropisomerism in biphenyls Hard
Which of the following biphenyls is optically active?
A -
B -
C -
D -

Explanation

Bulky ortho groups on both rings restrict rotation, creating axial chirality.

Detailed Solution

A substituted biphenyl can have a chiral axis when the steric (van der Waals repulsion) interaction between ortho substituents is sufficient to stop rotation of the aromatic rings relative to each other about the bond joining the two rings.

So the biphenyl with Br and I at all four ortho positions is optically active.

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