Step 1: Understanding the Concept:
In electrophilic aromatic substitution (EAS), the preferred site of attack is determined by the electronic nature of the substituents already present on the aromatic rings.
An electron-donating group (EDG) activates the ring and directs the electrophile to the ortho and para positions.
An electron-withdrawing group (EWG) deactivates the ring and directs the electrophile to the meta position. Step 2: Detailed Explanation:
The given molecule "x" consists of two aromatic rings connected by an amide linkage (\(-NH-CO-\)).
1. Left Ring: It is attached to the nitrogen atom (\(-NH-\)) of the amide group. The lone pair on Nitrogen is directly in conjugation with the ring (delocalized). This makes the group (\(-NHCOR\)) a strongly activating, ortho-para directing group.
2. Right Ring: It is attached to the carbonyl group (\(-CO-\)) of the amide. The carbonyl group is electron-withdrawing by resonance, making it a deactivating, meta-directing group.
Electrophiles preferentially attack the more electron-rich ring. Therefore, the attack will occur on the left ring.
In the left ring, the amido group directs to positions "p" (ortho) and "r" (para).
Due to the steric hindrance provided by the bulky amido group, the para position ("r") is more accessible and favored over the ortho position ("p").
Thus, the attack occurs predominantly at "r". Step 3: Final Answer:
The preferred site of attack is predominantly at "r".
