JEE Advanced · 2025 · 18 May 2025 · Paper 1 · Hydrocarbons

Consider the depicted hydrogen (H) in the hydrocarbons given below. The most acidic hydrogen (H) is

(A)(see structure)
(B)(see structure)
✓ Correct
(C)(see structure)
(D)(see structure)

Answer: (B)

Solution

The acidity of a hydrogen depends on the stability of the conjugate base formed after deprotonation. The most acidic hydrogen is the one whose removal leads to the most stable carbanion.

In option (B), the hydrogen is positioned such that its removal forms a conjugate base stabilized by resonance through the cyclopentadiene system. This cyclopentadienyl anion is aromatic (6 π electrons), making it exceptionally stable.

Therefore, option (B) has the most acidic hydrogen because it forms the most stable conjugate base.

JEE Advanced · 2025 · 18 May 2025 · Paper 1 · Single correct option

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