AIIMS 2019 Chemistry Aromatic Compounds MCQ Question
Identify structure of ‘P’ and ‘Q’ Correct order of pKa value is:
P= CH₃O—C₆H₄—C—CH₂—OH, Q= CH₃O—C₆H₄—C—CH₂—Br
P= CH₃O—C₆H₄—C—CH₂—O, Q= CH₃O—C₆H₄—C—CH₂Br
P= CH₃O—C₆H₄—C—CH₂—O, Q= CH₃O—C₆H₄—C—CH₂—Br
P= CH₃O—C₆H₄—C—CH₂—O, Q= CH₃O—C₆H₄—C—CH₂—Br
Correct Answer
Detailed Explanation
In option C, both compounds P and Q are derivatives of a substituted phenol, where P has a hydroxyl group (—OH) and Q has a bromine atom (—Br) attached to the same carbon chain. The presence of the electronegative bromine in Q stabilizes the conjugate base formed upon deprotonation, leading to a lower pKa value compared to P, which has the less electronegative hydroxyl group. Options A and B incorrectly represent the structures, as they either mislabel the functional groups or include incorrect substituents, which affects the pKa comparison. Understanding the influence of substituents on acidity is crucial for predicting pKa values in organic compounds.
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