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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3o3160

Sulfur mustard, , is hydrolysed in water. Select the correct statement(s).

  1. AReplacing sulfur by oxygen, , would greatly increase the rate because oxygen is more electronegative.
  2. BThe rate law is first order in the mustard and nearly independent of the concentration of added external nucleophiles.
  3. CThe rate-determining step is intramolecular attack of sulfur on the C-Cl carbon to give a cyclic episulfonium ion.
  4. DThe ring-opening of the episulfonium ion by water occurs with inversion at the carbon attacked.

Answer: B, C, D

Sulfur's lone pair displaces chloride (rate-determining and unimolecular in substrate), so the rate does not involve the external nucleophile. The strained three-membered sulfonium ion is opened by water in an SN2 step with inversion. Oxygen holds its lone pairs tightly and is a much poorer neighbouring group, so the ether is far less reactive, not more.
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