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JEE Advanced levelSingle correct optionDifficulty 3 of 3hc201

Assertion (A): 1,4-Addition of to buta-1,3-diene is favoured at higher temperature (about ). Reason (R): The 1,4-adduct is formed faster than the 1,2-adduct because bromide is closer to C4 of the allylic cation.

  1. ABoth A and R are true and R is the correct explanation of A
  2. BBoth A and R are true but R is not the correct explanation of A
  3. CA is true but R is false
  4. DA is false but R is true

Answer: C

A is true: at the higher temperature the reaction is reversible and the more stable 1,4-adduct (internal double bond) wins. R is false: the 1,2-adduct forms faster because bromide ion is closest to C2, the carbon that bears the positive charge in the main resonance form.
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