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JEE Main levelSingle correct optionDifficulty 2 of 3g3027

Dehydration of 2,2-dimethylcyclopentan-1-ol with concentrated proceeds through carbocations with rearrangement. The major alkene (most substituted) is:

  1. A1,2-dimethylcyclopent-1-ene
  2. B3,3-dimethylcyclopent-1-ene
  3. Ccyclopentylidene-methane (methylenecyclopentane)
  4. D1,5-dimethylcyclopent-1-ene

Answer: A

Loss of water gives the secondary ring cation next to a quaternary carbon. A methyl shift moves the charge to the tertiary ring carbon, 1,2-dimethylcyclopentyl cation. Loss of a proton gives the tetrasubstituted alkene 1,2-dimethylcyclopent-1-ene (Saytzeff).
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