Question

Which of the following is least reactive towards $S_{N}1$ ?

• A.
• B.
• C.
• D.

Answer 1

Answer: (A)

Here is least reactive towards $S_{N}1$ .

Rate of $S_{N}1\propto$ stability of carbocation



$\left(A\right)\Rightarrow$ Anti aromatic

$\left(B\right)\Rightarrow$ Non-aromatic (no resonance)

$\left(C\right)\Rightarrow$ Non-aromatic (resonance)

$\left(D\right)\Rightarrow$ Aromatic

Stability order

Aromatic > non-aromatic > anti-aromatic

So D > C > B > A.