Chemistry – Organic chemistry | e-Consult

Aromaticity in benzene arises from a special electronic structure resulting from the cyclic, planar arrangement of six pi electrons. These electrons are delocalised over the entire ring, creating a stable, symmetrical system. This delocalisation leads to a significant increase in the stability of benzene compared to a hypothetical cyclohexatriene with alternating single and double bonds. The delocalisation results in a lower overall energy for benzene, making it exceptionally stable.

This aromaticity significantly influences benzene's reactivity. Alkenes undergo addition reactions because the pi bond is a reactive site. However, the delocalised pi electrons in benzene are not readily available for addition. Instead, benzene predominantly undergoes electrophilic aromatic substitution reactions. This is because the electrophile can interact with the pi system without disrupting the aromaticity. The aromatic system is essentially 'protected' from addition, leading to a different reaction pathway.

Key points:

• Aromaticity = cyclic, planar, fully delocalised pi system.
• Increased stability compared to cyclohexatriene.
• Resistance to addition reactions.
• Preference for electrophilic aromatic substitution.