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JEE Main levelSingle correct optionDifficulty 2 of 3o4190

For the E2 reaction of 2-halobutanes with in ethanol the percentages of but-1-ene (rest but-2-ene) in this problem are: F 70, Cl 33, Br 31, I 30. The data show that:

  1. Athe poorer the leaving group, the larger the fraction of the Hofmann (less substituted) alkene
  2. Bthe better the leaving group, the larger the fraction of but-1-ene
  3. Cleaving group has no influence on the orientation of elimination
  4. DSaytzeff orientation is strongest for fluoride

Answer: A

Moving from I to F the leaving group becomes poorer and the but-1-ene fraction rises from 30% to 70%. A poor leaving group makes the transition state more carbanion-like and favours the more accessible, more acidic hydrogen, so Hofmann orientation increases.
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