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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3o3164

3-Phenylbutan-2-yl tosylates and related phenyl-bearing substrates solvolyse with participation of the phenyl ring. Select the correct statement(s).

  1. AA p-methoxy substituent on the ring increases the extent of phenyl participation.
  2. BThe phenyl ring attacks the carbon bearing the leaving group from the side opposite to it, forming a bridged phenonium ion.
  3. CIn acetic acid, (2S,3R)-3-phenylbutan-2-yl tosylate gives an essentially racemic acetate while (2S,3S)-3-phenylbutan-2-yl tosylate gives an optically active acetate.
  4. DThe rate enhancement arises because the phenyl ring withdraws electron density inductively from the carbinol carbon.

Answer: A, B, C

Participation by the aromatic pi electrons forms the spiro cyclohexadienyl (phenonium) ion. The (2S,3R) isomer gives a phenonium ion with a mirror plane (cis methyl groups), whose symmetric opening gives a racemate; the (2S,3S) isomer gives a chiral (trans) phenonium ion and a retained, optically active product. Electron-donating groups stabilise the phenonium ion and promote participation. An inductive withdrawal by phenyl would slow ionisation, not speed it.
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