Chemistry - GOC Question with Solution | TestHub

(A) allyl, (C) benzyl and (D) alpha-alkoxy cations all have a pi bond or lone pair next to ${\mathrm{C}}^{+}$.

In (B) a $\mathrm{C}{\mathrm{H}}_2$ group separates ${\mathrm{C}}^{+}$ from the $\mathrm{C}=\mathrm{C}$, so the empty p orbital cannot overlap with the pi bond.