Which of the following compounds will undergo $S_N1$ reaction at a fastest rate?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) →
SN1 reaction proceeds via carbocation intermediate.
Rate of SN1 reaction depends on stability of carbocation formed.
Order of carbocation stability: Tertiary > Secondary > Primary
Tertiary carbocation is most stable due to:
Greater hyperconjugation
Strong +I effect from alkyl groups
Thus, tertiary alkyl chloride undergoes SN1 reaction fastest.
Option 1: Secondary alkyl chloride Forms secondary carbocation. Moderate stability. Slower than tertiary. Incorrect.
Option 2: Primary alkyl chloride Forms primary carbocation. Very unstable. Very slow SN1. Incorrect.
Option 3: Tertiary alkyl chloride --- Forms highly stable tertiary carbocation. Fastest SN1 reaction. Correct.
Option 4: Secondary alkyl chloride Forms secondary carbocation. Slower than tertiary. Incorrect.