Question

The increasing order of reactivity of the following bromides in $S_{N}1$ reaction is

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

Answer 1

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

From the given compound, carbocation formed by (III) is most stable because it aromatic in nature with 6 $\pi$ electrons.
Compound (II) is the least stable, because carbocation formed is antiaromatic in nature.
Comparing (I) and (IV)
Carbocation formed by (I) is allylic ion so there will be delocalisation of electron and it makes it stable than (IV)