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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3o3272

The enantiopure epoxide shown is opened (i) with sodium methoxide in methanol and (ii) with a catalytic amount of in methanol. Assume the standard regiochemistry: basic opening at the less hindered carbon, acid-catalysed opening at the carbon that better stabilises positive charge. Select all correct statements about the major products.

  1. AIn (i) the stereocentre keeps its spatial arrangement
  2. BIn (i) the product is (S)-1-methoxypropan-2-ol
  3. CIn (ii) the major product is (S)-2-methoxypropan-1-ol, formed with inversion
  4. DBoth (i) and (ii) give the same constitutional isomer

Answer: A, C

The compound is (R)-methyloxirane. In (i) the nucleophile attacks CH2, so the stereocentre is untouched and its arrangement is retained; the product is R-1-methoxypropan-2-ol (RDKit), so the claim that it is (S) is wrong. In (ii) methanol attacks the secondary carbon with inversion, giving (S)-2-methoxypropan-1-ol. The two conditions give different constitutional isomers. Correct: first and third.
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