Here’s a explanation of how benzene undergoes nitration in an easy-to-understand way:
Step 1: Formation of the Electrophile
- Nitration requires a strong electrophile called the nitronium ion (NO₂⁺).
- This is generated by mixing concentrated nitric acid and sulfuric acid.
- The nitronium ion is highly reactive and ready to attack the benzene ring.
Step 2: Attack on the Benzene Ring
- Benzene has a cloud of π-electrons that is rich in electrons.
- One of the carbons in the benzene ring donates electrons to the nitronium ion, forming a temporary intermediate called a sigma complex (arenium ion).
- During this step, the aromaticity of benzene is temporarily lost.
- This step is slow and rate-determining because breaking aromatic stability requires energy.
Step 3: Restoration of Aromaticity
- The intermediate loses a hydrogen atom from the carbon that bonded to the nitronium ion.
- This step restores the aromaticity of the benzene ring, giving nitrobenzene as the product.
Summary
- Nitration is an electrophilic aromatic substitution reaction.
- Benzene reacts with the nitronium ion (NO₂⁺).
- The reaction occurs in three main steps:
- Formation of electrophile
- Attack on the benzene ring forming sigma complex
- Loss of hydrogen to restore aromaticity