Match the major products obtained in the reactions given in List-I with the corresponding structures in List-II and choose the correct option.

Correct Answer: P → 2; Q → 1; R → 5; S → 4

Let us analyze each reaction given in List-I step-by-step by examining the reactant structure, reagents, and corresponding mechanism to identify the major products in List-II.

1. Reaction (P):

Reactant (P) is an aldoxime: 2-bromo-5-nitrobenzaldehyde oxime.

Reagent: aqueous NaOH

Mechanism: Hydroxide ion (OH^-) acts as a base and deprotonates the oxime hydroxyl proton (-OH), forming an oximate anion. This promotes elimination of water (dehydration of the aldoxime) to yield a nitrile group (-CN). Under these conditions, the bromine atom at the ortho position remains unattacked or dehydration is the primary pathway yielding 2-bromo-5-nitrobenzonitrile.

Therefore, reaction (P) corresponds to structure (2).

2. Reaction (Q):

Reactant (Q) is the same aldoxime: 2-bromo-5-nitrobenzaldehyde oxime.

Reagents: 1. (CH₃CO)₂O (acetic anhydride) followed by 2. Na₂CO₃

Mechanism: Acetic anhydride acylates the -OH group of the oxime to form an oxime acetate (-O-COCH₃). Upon treatment with base, it undergoes elimination of acetic acid to form the nitrile (-CN). Concurrently or sequentially, nucleophilic aromatic substitution (S_NAr) occurs at the activated ortho position (activated by the strongly electron-withdrawing -NO₂ and -CN groups), replacing the bromine atom (-Br) with a hydroxyl group (-OH).

Therefore, the major product is 2-hydroxy-5-nitrobenzonitrile, which corresponds to structure (1).

So, reaction (Q) corresponds to structure (1).

3. Reaction (R):

Reactant (R) is a ketoxime: 1-(2-bromo-5-nitrophenyl)ethan-1-one oxime.

Reagent: aqueous NaOH

Mechanism: Ketoximes lack an acidic aldoxime CH proton for elimination to form nitriles. Under mild aqueous NaOH treatment without a strong activating reagent/acid catalyst for Beckmann rearrangement or intramolecular cyclization, the ketoxime does not react significantly and is recovered unchanged (or remains as the ketoxime structure).

Thus, reaction (R) matches the unreacted/original ketoxime structure shown in (5).

So, reaction (R) corresponds to structure (5).

4. Reaction (S):

Reactant (S) is the O-acetylated derivative of the ketoxime: 1-(2-bromo-5-nitrophenyl)ethanone O-acetyl oxime.

Reagent: aqueous Na₂CO₃

Mechanism: The acetate group (-OCOCH₃) is a good leaving group. Deprotonation or intramolecular nucleophilic displacement by the oxime oxygen or intramolecular attack by the aromatic ring oxime derivative leads to intramolecular displacement of bromine (intramolecular S_NAr cyclization), forming a 1,2-benzisoxazole derivative (specifically 3-methyl-5-nitrobenzo[c]isoxazole / 3-methyl-5-nitroisoxazole ring system).

Therefore, reaction (S) yields the cyclic product corresponding to structure (4).

Matching Summary:

• P → 2

• Q → 1

• R → 5

• S → 4