Explain `SN^(1)` reaction

Explanation

`SN^(1)` : Substitution nucleophilic unimolecular reaction : In this reaction the first step is the formation of stable carbonium ion. This step is slow and is the rate determining step . The alkyl halides which form stable carbonium ion follow `SN^(1)` reaction .

The order of reactivity of alkyl halides towards `SN^(1)` reaction .
Tertiary halide `gt` Secondary halide `gt` Primary halide `gt CH_(3) - X`
Benzyl halide and alkyl halides are primary but participate in `SN^(1)` mechanism due to the formation of stable benzyl and allyl carbonium ions (Benzyl and allyl carbonium ions are stabilised due to resonance).