The correct answer is Option (3) → p-bromoacetanilide
Acetanilide consists of an acetyl group ($-NHCOCH_3$) attached to a benzene ring. This group influences the reaction in two main ways:
- Activating and Ortho/Para Directing: The nitrogen atom has a lone pair of electrons that it can donate into the benzene ring via resonance, making the ring more reactive toward electrophiles like bromine. This resonance specifically increases electron density at the ortho and para positions.
- Steric Hindrance: Unlike a simple amino group ($-NH_2$), the acetyl group is quite bulky. This "steric bulk" creates significant crowding at the ortho positions, making it difficult for the large bromine atom to attach there.
- The Result: Because the para position is far away from the bulky acetyl group, the bromine atom can attach there with much less resistance, making it the major product.
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