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JEE Main levelSingle correct optionDifficulty 2 of 3g2251

The structures shown are four anions, each obtained from the molecule drawn by removing one proton. Which anion results from loss of the most acidic hydrogen?

  1. AStructure A
  2. BStructure B
  3. CStructure C
  4. DStructure D

Answer: B

The molecule is but-3-yn-1-ol. The O-H hydrogen (alcohol, pKa about 16) is more acidic than the terminal alkyne C-H (about 25), and far more than sp3 C-H bonds (about 45 to 50). The alkoxide is therefore the favoured anion.
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