Question

The correct stability order of the following species is:

• A. (II) > (IV) > (I) > (III)
• B. (I) > (II) > (III) > (IV)
• C. (II) > (I) > (IV) > (III)
• D. (I) > (III) > (II) > (IV)

Answer 1

The correct option is D (I) > (III) > (II) > (IV)

The $\sigma$- electron of 6 $\alpha$ C-H bonds are delocalised by hyperconjugation with p-orbitals of carbocation in (I) stabilizing it most stable. Also, Lone pair electrons of oxygen delocalize to carbocation in (I) making it most stabilized.
The $\sigma$- electron of 3 $\alpha$ C-H bonds are delocalised by hyperconjugation with p-orbitals of carbocation in (III) stabilizing it second most stable.
Lone pair electrons of oxygen delocalize to carbocation in (III) making it second most stabilized.

(II) has a secondary carbocation which is more stable than the primary carbocation in (IV).

Therefore, overall stability order is : I > III > II > IV