See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: In electrophilic aromatic substitution (EAS), the directing effect of substituents determines the position (ortho/para vs meta) where the incoming electrophile (NO2+) attacks. Meta directors are electron-withdrawing groups (EWG) that destabilize the ortho and para intermediates, leading to preferential meta substitution. Ortho/para directors are electron-donating groups (EDG). Step 1 - Analyze each option: (a) Toluene has a methyl group (-CH3), which is an EDG via hyperconjugation and induction. It is an ortho/para director. Nitration gives predominantly ortho + para products (~95%), with very little meta (~5%). (b) Aniline has an amino group (-NH2), which is normally a strong ortho/para director. However, under acidic conditions (HNO3/H2SO4), the -NH2 group gets protonated to form -NH3+. The -NH3+ group is a strong electron-withdrawing group (EWG) and acts as a meta director. Therefore, nitration of aniline under these strongly acidic conditions gives a significantly higher percentage of meta product compared to the other options. (c) Benzene has no substituent, so it has no directing effect. All positions are equivalent and give only one monosubstitution product. There is no concept of meta vs ortho/para selectivity. (d) Isopropyl benzene (cumene) has an isopropyl group (-CH(CH3)2), which is an EDG via hyperconjugation and induction, making it an ortho/para director. Nitration gives predominantly ortho + para products with little meta. Step 2 - Identify which gives maximum meta product: Among the options, aniline (b) under acidic conditions (HNO3/H2SO4) has its -NH2 protonated to -NH3+, a strong meta director. This gives the maximum percentage of meta-nitroaniline product. Step 3 - Why other options fail: - Toluene and isopropyl benzene are ortho/para directors giving mostly ortho/para products. - Benzene gives a single product with no positional selectivity issue. - Only aniline, due to protonation of -NH2 under acidic nitrating conditions, acts as a meta director and gives maximum meta product. Therefore, the correct answer is B.