Identify the correct order of reactivity of the following compounds towards the S _ N 1 reaction: (I) (II) (III)

Step-by-step solution

The reactivity of a compound towards the S _ N 1 reaction depends on the stability of the carbocation intermediate formed after the departure of the leaving group ( Cl ⁻ ). In compound (I), the loss of Cl ⁻ generates a carbocation at the C4 position. The oxygen atom donates its lone pair of electrons to the conjugated system, resulting in a cyclic, planar structure with 6 electrons. This forms the pyrylium ion, which is aromatic and highly stable. In compound (II), the loss of Cl ⁻ generates a carbocation that is s