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JEE Main levelSingle correct optionDifficulty 2 of 3g2027

Which of the following hydrocarbons is the most acidic?

  1. Acyclohepta-1,3,5-triene
  2. Bcyclopenta-1,3-diene
  3. Ccyclohexane
  4. Dcyclohexa-1,3-diene

Answer: B

Loss of H+ from cyclopenta-1,3-diene gives the cyclopentadienyl anion, which is planar, cyclic, fully conjugated and has 6 pi electrons, so it is aromatic (pKa about 16). The other hydrocarbons give non-aromatic carbanions (pKa 35-50).
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