Following reactions are given by haloarenes :

`=>` Aryl halides are extremely less reactive towards nucleophilic substitution reactions due to the following reasons :

(i) `color{green}("Resonance effect ")` : In haloarenes, the electron pairs on halogen atom are in conjugation with `color{red}(π)`-electrons of the ring and the resonating structures as shown in fig.1 are possible.

`=>` `color{red}(C—Cl)` bond acquires a partial double bond character due to resonance.

● Therefore, the bond cleavage in haloarene is difficult than haloalkane and therefore, they are less reactive towards nucleophilic substitution reaction.

(ii) `color{green}("Difference in hybridisation of carbon atom in C—X bond")` : In haloalkane, the carbon atom attached to halogen is `color{red}(sp^3)` hybridised while in case of haloarene, the carbon atom attached to halogen is `color{red}(sp^2)`-hybridised. See fig.2.

`=>` The `color{red}(sp^2)` hybridised carbon with a greater `color{red}(s)`-character is more electronegative and can hold the electron pair of `color{red}(C—X)` bond more tightly than `color{red}(sp^3)`-hybridised carbon in haloalkane with less `color{red}(s)`-chararcter.

● `color{red}(C—Cl)` bond length in haloalkane is `177` pm while in haloarene is `169` pm.

● Because it is difficult to break a shorter bond than a longer bond, therefore, haloarenes are less reactive than haloalkanes towards nucleophilic substitution reaction.

(iii) `color{green}("Instability of phenyl cation ")` : In case of haloarenes, the phenyl cation formed as a result of self-ionisation will not be stabilised by resonance and therefore, `color{red}(S_N 1)` mechanism is ruled out.

(iv) Because of the possible repulsion, it is less likely for the electron rich nucleophile to approach electron rich arenes.

`=>` Chlorobenzene can be converted into phenol by heating in aqueous sodium hydroxide solution at a temperature of `623K` and a pressure of `300` atmospheres. See fig.1.

`=>`The presence of an electron withdrawing group `color{red}((-NO_2))` at ortho- and para-positions increases the reactivity of haloarenes. See fig.2.

`=>` The effect is pronounced when `color{red}((-NO_2))` group is introduced at ortho- and para- positions.

`=>` No effect on reactivity of haloarenes is observed by the presence of electron withdrawing group at meta-position.

`=>` Mechanism of the reaction is as depicted in fig.3.

`=>` Haloarenes undergo the usual electrophilic reactions of the benzene ring such as halogenation, nitration, sulphonation and Friedel-Crafts reactions.

`=>` Halogen atom besides being slightly deactivating is `color{red}(o, p)`-directing; therefore, further substitution occurs at ortho- and para-positions with respect to the halogen atom.

`=>` The `color{red}(o, p)`-directing influence of halogen atom can be easily understood if we consider the resonating structures of halobenzene as shown in fig.1.

`=>` Due to resonance, the electron density increases more at ortho- and para-positions than at meta-positions.

`=>` Further, the halogen atom because of its `color{red}(–I)` effect has some tendency to withdraw electrons from the benzene ring.

`=>` Therefore, the ring gets somewhat deactivated as compared to benzene and hence the electrophilic substitution reactions in haloarenes occur slowly and require more drastic conditions as compared to those in benzene.

`=>` Electrophilic reactions given by haloarenes is shown in fig.2.

`color{green}("Wurtz-Fittig Reaction ")`: A mixture of an alkyl halide and aryl halide gives an alkylarene when treated with sodium in dry ether and is called Wurtz-Fittig reaction. See fig.1.

`color{green}("Fittig Reaction ")` : Aryl halides also give analogous compounds when treated with sodium in dry ether, in which two aryl groups are joined together. It is called Fittig reaction. See fig.2.