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JEE Main levelSingle correct optionDifficulty 2 of 3o1140

Ketone protection is carried out more efficiently with ethylene glycol than with two molecules of methanol. The main reason is that

  1. Aethylene glycol is a much stronger acid and protonates the carbonyl
  2. Bethylene glycol is converted completely into its alkoxide ion
  3. Cthe second C-O bond forms by an intramolecular ring closure, with much less loss of entropy
  4. Dethylene glycol reduces the carbonyl to a carbinol first

Answer: C

The first O-H adds intermolecularly in both cases. For the diol, the second OH is held near the oxocarbenium ion by the chain and closes a five-membered ring, so the entropy cost is small. With methanol a second molecule must be brought in, which is less favourable.
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