Electrophilic and nucleophilic substitution in aromatic

1 Substitution of hydrogen, p. 167 6.10.2 Substitution of atoms other than hydrogen, p. 169 6.10.3 Substitution via aryne intermediates p. 173. 

Reference has already been made to the structure of benzene and, in particular, to its delocalised -ir orbitals (p. 15) the concentration of negative charge above and below the plane of the ring-carbon atoms is thus benzene s most accessible feature  

This concentration of charge might be expected to shield the ring carbon atoms from the attack of nucleophilic reagents and, by contrast, to promote attack by cations, X , or electron-deficient species, i.e. by electrophilic reagents this is indeed found to be the case. 

It might be expected that the first phase of reaction would be interaction between the approaching electrophile and the delocalised n orbitals and, in fact, so-called n complexes such as (1) are formed  

The gain in stabilisation in going from (2) — (4) helps to provide the energy required to break the strong C—H bond that expulsion of H necessitates in the reaction of, for example, HC1 with alkenes (p. 184) there is no such factor promoting substitution and addition reactions are therefore the rule. 

---

Electrophilic and nucleophilic substitution in aromatic systems ring fission to yield the more familiar 1-naphthol (104) ... 

---