Question

The correct order of stability is:

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

Answer 1

The correct option is B III > II > I > IV

It has zero $\alpha$-H. Therefore, the carbocation is only stabilised by $+I$ effect.
It has 3 $\alpha$-H. Therefore, it will be more stable than I.
It has 7 $\alpha$-H. Therefore, it will be more stable than I and II both.
Bridgehead carbocation is unstable. Therefore, structure IV carbocation is the least carbocation.

Therefore, the stability order of carbocations is:
III > II > I > IV