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JEE Main · 2022 · 28 Jul 2022 · Shift 1 · Aldehydes Ketones and Carboxylic Acids

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Among the following marked proton of which compound shows lowest value?
  1. (A)(see structure)
  2. (B)(see structure)
  3. (C)(see structure)
    ✓ Correct
  4. (D)(see structure)

Answer: (C)

Solution

The compound with the lowest pKₐ value is the one whose conjugate base is most stable. In option (C), the marked proton is α to both a carbonyl group and a benzyl group. Removal of this proton gives a carbanion stabilized by resonance with both the carbonyl group and the benzene ring, making it the most acidic (lowest pKₐ). Options (A) and (D) have carboxylic acid protons which are less acidic than the α-proton in (C), and option (B) has a simple α-hydrogen with only carbonyl stabilization.

JEE Main · 2022 · 28 Jul 2022 · Shift 1 · Single correct option

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