Question

The correct stability order for 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

(I) and (III) are resonance stabilised by the oxygen group so they are more stable than (II) and (IV).
$\text{Stability of carbocation}\propto \text{Number of}\alpha -H$

(IV) is least stabilised because it is a primary carbocation.
Comaparing (I) and (II)
(I) is tertiary carbocation and it is resonance stabilised by oxygen atom.
(III) is also resonance stabilised but it is a secondary carbocation. Since tertiary carbocation is more stable than secondary, (I) is the more stable carbocation than (III)


Thus, order of stability of the carbocation is
(I) > (III) > (II) > (IV)