Why does Benzene Undergo Only Electrophilic Substitution Reactions?

Why does benzene undergo an electrophilic substitution reaction? This property is due to the remarkable stability of benzene as the six delocalized electrons form clouds of electrons. Instead of forming three fixed C == C bonds, they form a delocalized ring which gives greater stability to benzene, which destroys degeneration of delocalized electrons in benzene Can be seen. Comparing the structures of benzene and 1,3,5-cyclohexanetriene, it can be seen that the same enthalpy change causes destruction of the delocalized ring of benzene and the 1,3,5 π bond of 1,3,5-cyclohexanetriene is expected. However, in real life it is about 150 kJ / mol.

As with benzene, naphthalene can undergo electrophilic aromatic substitution. In many electrophilic aromatic substitution reactions, naphthalene is more reactive than benzene and reacts under milder conditions than benzene. For example, both benzene and naphthalene react with chlorine in the presence of ferric chloride or aluminum chloride catalysts, but naphthalene and chlorine can react without catalyst, to form 1-chloronaphthalene. Likewise, both benzene and naphthalene can be alkylated using a Friedel-Crafts reaction, but naphthalene can also be alkylated by reaction with olefins or alcohols with sulfuric acid or phosphoric acid as a catalyst.

Why does benzene undergo an electrophilic substitution reaction? This property is due to the remarkable stability of benzene as the six delocalized electrons form clouds of electrons. Instead of forming three fixed C == C bonds, they form a delocalized ring which gives greater stability to benzene, which destroys degeneration of delocalized electrons in benzene Can be seen. Comparing the structures of benzene and 1,3,5-cyclohexanetriene, it can be seen that the same enthalpy change causes destruction of the delocalized ring of benzene and the 1,3,5 π bond of 1,3,5-cyclohexanetriene is expected. However, in real life it is about 150 kJ / mol.

Haloareanes undergo general electrophilic reactions of benzene rings such as halogenation, nitration, sulfonation and Friedel-Crafts reactions. In addition to being slightly deactivated, the halogen atom is in the o, p orientation; therefore further substitution takes place in the ortho and para positions relative to the halogen atom. Given the resonance structure of halogenated benzene, we can easily understand the effect of halogen atoms in the o and p directions. Due to resonance, the electron density increases at the ortho and para positions than the element. In addition, halogen atoms tend to extract electrons from the benzene ring due to their "I effect". As a result, the ring becomes somewhat inert compared to benzene, so electrophilic substitution reactions in halogenated aromatic hydrocarbons occur slowly, requiring more stringent conditions compared to benzene.