In each of the following pairs of compounds, identify the compound which will undergo `S_(N)1` reaction faster?

Explanation

(i) The reactivity in `S_(N)1` reactions depends upon the stability of the intermediate carbocation which an alkyl halide gives on ionization Thus.

Since `3^(@)` carbocations are more stable than `2^(@)` carbocations, therefore will react faster than in `S_(N)1` reactions.
(ii) Benzyl chloride readily forms benzyl cation
which is stabilzied by resonance. in contrast, chlorobenzene does not form phenyl cation because it is highly unstable, thus, benzyl chloride undergoes `S_(N)1` reaction faster than chlorobenzene.