Question:medium

The decreasing order of reactivity of the following alkenes towards HBr addition is: \(\text{CH}_3-\text{CH}=\text{CH}_2 \, (\text{I}), \quad \text{CF}_3-\text{CH}=\text{CH}_2 \, (\text{II}), \quad \text{MeOCH}=\text{CH}_2 \, (\text{III}),\) alkenes, \((\text{IV}) \)

Updated On: Jan 29, 2026
  • \(I>II>III>IV\)
  • \(II>IV>I>III\)
  • \(III>IV>I>II\)
  • \(III>I>II>IV\)
Show Solution

The Correct Option is D

Solution and Explanation

The reactivity of alkenes in HBr addition is determined by the stability of the carbocation intermediate:

  • \(\text{- MeOCH=CH}_2\) (III): Most reactive due to resonance stabilization from the methoxy group, forming a stable carbocation.
  • \(\text{- CH}_3\text{-CH=CH}_2\) (I): Moderately reactive; forms a secondary carbocation.
  • \(\text{- CF}_3\text{-CH=CH}_2\) (II): Least reactive; forms a destabilized carbocation due to the electron-withdrawing CF3 group.
  • \(\text{- CH}_3 - \overset{\text{O}}{\overset{||}{\text{C}}} - \text{CH=CH}_2\) (IV): Forms a sterically hindered carbocation, resulting in the lowest reactivity.

Therefore, the reactivity order is III>I>II>IV.

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