Following are the four molecules "P", "Q", "R" and "S": Which one among the four molecules will react with H-Br(aq) at…
Hydrocarbons · Class 11 · JEE Main Previous Year Question
Following are the four molecules "P", "Q", "R" and "S": Which one among the four molecules will react with at the fastest rate?
- a✓
Q
- b
R
- c
P
- d
S
Q
Step 1: Understand the rate-determining step
Electrophilic addition of to alkenes proceeds via carbocation formation as the rate-determining step. The compound that generates the most stable carbocation will be the one reacting fastest.
Answer: Option (a) — Q
Key Points to Remember:
- Rate of electrophilic addition ∝ stability of carbocation intermediate
- Exocyclic alkenes (like methylenecyclopentane) form very stable ring-junction carbocations
- Tertiary > secondary > primary carbocation stability
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