Chemistry · Carboxylic Acids: Acidic strength and factors affecting it

Among the following, the strongest acid is :

Among the following, the strongest acid is :

  • A. \( C_{6} H_{5} C H_{2} N H_{2} \)
  • B. \( C_{6} H_{5} \) СООН
  • C. \( m-C H_{3} O C_{6} H_{4} C O O H \)
  • D. \( p-C H_{3} O C_{6} H_{4} \) COOH

Step-by-step solution

Option A is benzylamine, a base, not an acid. Among benzoic acid (B), m-methoxybenzoic acid (C), and p-methoxybenzoic acid (D), the methoxy group is electron-donating by resonance (+R) and electron-withdrawing by inductive effect (-I). At the meta position, the +R effect is minimal, so the -I effect dominates, making m-methoxybenzoic acid more acidic than benzoic acid. At the para position, the +R effect is strong, decreasing acidity. Thus, the strongest acid is m-methoxybenzoic acid.
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