AIIMS 2019 Chemistry Effect of Substituents MCQ Question
The given compounds are shown below. In compound (a), NO₂ possesses the -M effect at para position due to which it is highly acidic than other three compounds. The compound (b) has intermolecular hydrogen bonding and it is less acidic than (a). In compound (d), there is absence of an electron donating group, due to which it is more acidic than compound (c), which has electron donating methyl group. Therefore, the correct order of acidic nature is a > b > d > c.
(a)
(b)
(c)
(d)
Correct Answer
Detailed Explanation
Option B is correct because compound (b) exhibits intermolecular hydrogen bonding, which stabilizes its structure and reduces its acidity compared to compound (a), where the -NO₂ group exerts a strong -M effect, enhancing acidity. In contrast, compound (c) has a methyl group, which is an electron-donating group that decreases acidity by destabilizing the conjugate base, while compound (d) lacks such a group, making it more acidic than (c) but less than (b) due to the absence of hydrogen bonding. Thus, the order of acidity is influenced by the presence of electron-withdrawing or donating groups and hydrogen bonding interactions.
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