Question

Maximum extent of steric inhibition of resonance can be expected in

• A.
• B.
• C.
• D.

Answer 1

The correct option is C

When a bulky group is present in the ortho position it will force them out of planarity due to steric force between group. Since, they are out of plane, it will reduce or prevent the delocalisation of electron (Resonance) with the plane. This effect is known as SIR (Steric Inhibition of Resonance ). This effect occurs when a bulky group is present in ortho position.
In option (a), (b) and (d) we have alkyl group in para and meta position. Hence it won't show steric inhibition of resonance.
Whereas, option (c) has methyl group in both ortho position, so due to presence of bulky group in ortho, its steric repulsion forced itself out of the plane so that it won't involve resonance with phenyl ring. Hence, this compound has maximum extent of SIR ( Steric Inhibition Resonance) effect.