Two isomers (A) and (B) with Molar mass 184 g/mol and elemental composition C, 52.2 %; H, 4.9% and Br 42.9 % gave benzoic acid and p-bromobenzoic acid, respectively on oxidation with KMnO4. Isomer ' A ' is optically active and gives a pale yellow precipitate when warmed with alcoholic AgNO3. Isomer ' A ' and ' B ' are, respectively :
(A)H3C−CHBr−C6H5 and (see structure)A
(B)(see structure) and (see structure)AB
(C)H3C−CHBr−C6H5 and (see structure)A✓ Correct
(D)(see structure) and H3C−CHBr−C6H5A
Answer: (C)
Solution
Isomer A must be H3C−CHBr−C6H5 (1-bromo-1-phenylethane) because:
It is optically active (has a chiral carbon)
Gives pale yellow precipitate with alcoholic AgNO3 (secondary alkyl bromide)
Oxidation with KMnO4 gives benzoic acid (the methyl group is oxidized)
Isomer B is p-bromoethylbenzene (4-bromoethylbenzene) because:
It gives p-bromobenzoic acid on oxidation
The ethyl side chain is oxidized to carboxylic acid while the Br remains on the para position
Therefore, the answer is option (C).
JEE Main · 2022 · 29 Jun 2022 · Shift 2 · Single correct option
