Vinyl chloride does not give `S_(N)` reaction but alkyl chloride gives. Explain.

Answer

In Vinyl chloride `C-CI` bond is stable due to resonance (as in chlorobenzene)
`(##ALN_CHM_C08_E01_092_A01##)`
Hence `S_(N)` reaction in which `CI` is replaced by nucleophile is not possible. In addition to this, `sp^(2)`-hybridised carbon is more acidic than `sp^(3)`-carbon, hence removal of proton `(H^(+))` is easier than removal of halide `(CI^(-))`
In alkyl chloride, `S_(N)` reaction is easier since allyl carbocation formed after removal of `CI^(-)` is stabilised by resonance.
`CH_(2)=CHCH_(2)CO rarr CH_(2)=underset("Allyl carbocation")overset(o+)(CHCH_(2)+CI^(-))`
`(##ALN_CHM_C08_E01_092_A02##)`