Question

Which is more reactive chlorobenzene and chloroethane in the nucleophilic substitution and why?

Answer 1

Chlorobenzene is less reactive towards nucleophilic substitution reaction because of the following reasons:
1. The hybridization of carbon in chlorobenzene is $s{p}^2$, therefore, $s{p}^2$ is more electronegative than $s{p}^3$ which leads to the release of electrons in a lesser amount which makes it less Polar i.e less polar C-Cl Bond, hence more difficult to break.
2. Resonance effect: The electron pair on the chlorine atom is in conjugation with the electrons of the benzene ring which results in the following resonance structures:

This results in delocalization of the electrons of the C - Cl bond and a partial double bond character develop in the bond, which makes it difficult for the Nucleophile to cleave the C - Cl bond. That's why it is less reactive towards nucleophile or nucleophilic substitution reactions.
Chloroethane is more reactive towards nucleophilic substitution reactions since it is an alkyl halide. C-Cl bond is polar due to the $s{p}^3$ hybridization.
Among chlorobenzene and chloroethane, chloroethane is more reactive towards nucleophilic substitution.