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JEE Main levelSingle correct optionDifficulty 2 of 3o3135

2-Chloroethyl ethyl sulfide, , hydrolyses in water much faster than a typical primary chloride such as 1-chlorobutane, and the rate is independent of the concentration of added hydroxide. The best explanation is

  1. Ahydroxide attacks sulfur first and then displaces chloride
  2. Bslow intramolecular attack by sulfur gives a cyclic episulfonium ion, which is then opened rapidly
  3. Cthe primary carbocation is stabilised by hyperconjugation with sulfur
  4. Dthe C-Cl bond is weakened by the +I effect of the ethyl group

Answer: B

Sulfur is a good internal nucleophile. Intramolecular displacement of chloride, forming the cyclic episulfonium ion, is rate-determining and unimolecular in substrate, so added hydroxide cannot change the rate. A free primary cation would be too unstable to explain the speed.
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