Question

Which of the following compounds is most reactive in SN$_1$ reaction? 

• A. Option a
• B. Option b
• C. Option c
• D. Option d

Hint:

SN\(_1\) rate \( \propto \) carbocation stability:
\[ \text{Benzylic/Allylic} > 3^\circ > 2^\circ \gg 1^\circ > \text{Vinylic} \]
Resonance stabilization dominates.

Answer 1

The Correct Option is B

Concept:
SN\(_1\) reactivity depends on carbocation stability:
Resonance stabilization increases stability
Allylic and benzylic carbocations are highly stable
Vinylic carbocations are unstable
Step 1: Compare options
(B) Forms highly resonance-stabilized allylic carbocation
(A) Less resonance delocalization
(C) Only secondary carbocation
(D) Vinylic carbocation unstable
Conclusion:
Most stabilized carbocation \( \Rightarrow \) fastest SN\(_1\).