See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1 - Friedel-Crafts acylation with isobutyryl chloride: Benzene reacts with (CH3)2CH-C(=O)-Cl / AlCl3 to give isobutyrophenone, i.e., (CH3)2CH-C(=O)-C6H5 (4-methylacetophenone precursor, actually phenyl isopropyl ketone: C6H5-CO-CH(CH3)2). Step 2 - Clemmensen reduction: The ketone C6H5-CO-CH(CH3)2 is reduced to the alkane C6H5-CH2-CH(CH3)2, i.e., isobutylbenzene (4-methylbenzyl... actually it is (2-methylpropyl)benzene = isobutylbenzene: C6H5-CH2-CH(CH3)2). Step 3 - Friedel-Crafts acylation with acetyl chloride: Isobutylbenzene reacts with CH3-C(=O)-Cl / AlCl3 to give para-acetyl isobutylbenzene: the acetyl group goes para to the isobutyl group, giving 4-(2-methylpropyl)acetophenone, i.e., (CH3CO)-C6H4-CH2-CH(CH3)2 (para). Step 4 - NaCN / H2SO4: This converts the methyl ketone (COCH3) via a cyanohydrin or, more precisely, this is a Strecker-type or nitrile formation. Actually, NaCN with H2SO4 on a ketone ArCOCH3: under acidic conditions with NaCN, the ketone ArCOCH3 undergoes nucleophilic addition of CN- to give a cyanohydrin: Ar-C(OH)(CH3)-CN. Actually the reagent sequence suggests: the acetyl group ArCOCH3 reacts with NaCN to give Ar-C(OH)(CN)(CH3), a cyanohydrin. Step 5 - Red P + HI / H3O+: Red P + HI removes the OH (deoxygenation) from the cyanohydrin to give Ar-CH(CH3)-CN, and H3O+ hydrolyzes the nitrile to carboxylic acid: Ar-CH(CH3)-COOH. Here Ar = 4-(2-methylpropyl)phenyl = 4-isobutylphenyl. So the final product is: (CH3)2CH-CH2-C6H4-CH(CH3)-COOH (para substitution), which is 2-(4-isobutylphenyl)propanoic acid = Ibuprofen. This matches option (b): CH3-CH(CH3)-CH2-(para-phenylene)-CH(CH3)-CO2H, i.e., the isobutyl group [CH3CH(CH3)CH2-] at the para position and the -CH(CH3)-CO2H group on the other side of the ring. Option (a) is wrong because it has an ethyl group instead of isobutyl. Option (c) has no carboxylic acid. Option (d) lacks the isobutyl chain and methyl on the acetic acid carbon. Therefore, the correct answer is B.