Reactivity of Polycyclic Benzenoid Hydrocarbons

Apply the strategy discussed above for the synthesis of 2-nitrobenzenamine to a synthesis of 4-acetyl-2-chlorophenol, starting with phenol. 

In this section, we shall use resonance forms to predict the regioselectivity and reactivity of polycyclic aromatic molecules (Section 15-5), using naphthalene as an example. Some biological impfications of the reactivity of these substances will be explored in Section 16-7. 

The aromatic character of naphthalene is manifest in its reactivity It undergoes electrophilic substitution rather than addition. For example, treatment with bromine, even in the absence of a catalyst, results in smooth conversion into 1-bromonaphthalene. The mild conditions required for this process reveal that naphthalene is activated with respect to electrophilic aromatic substitution. 

Other electrophilic substitutions also are readily achieved and, again, are highly selective for reaction at Cl. For example. 

The highly delocalized nature of the intermediate explains the ease of attack. The cation can be nicely pictured as a hybrid of five resonance forms. 

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