Introduction of a nitro group (–NO₂) in a molecule is called ?

Nitration is a fundamental chemical reaction in organic chemistry that involves the introduction of a nitro group (–NO₂) into an organic molecule. This process is most commonly applied to aromatic compounds such as benzene and its derivatives, where it serves as an example of electrophilic aromatic substitution.

The typical nitration mixture consists of concentrated nitric acid (HNO₃) and concentrated sulfuric acid (H₂SO₄). Sulfuric acid acts as a catalyst and dehydrating agent, helping to generate the nitronium ion (NO₂⁺) — the actual electrophile responsible for attacking the aromatic ring.

Formation of nitronium ion:
HNO₃ + 2H₂SO₄ → NO₂⁺ + H₃O⁺ + 2HSO₄⁻

Once formed, the nitronium ion attacks the π-electron-rich aromatic ring, replacing one hydrogen atom with a nitro group. For example, in the nitration of benzene:
C₆H₆ + HNO₃ → C₆H₅NO₂ + H₂O

Examples of nitration reactions:

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  Benzene → Nitrobenzene

  
  


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  Toluene → Nitrotoluene

  
  


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  Phenol → Nitro phenol

  
  

Nitration reactions are widely used in both industrial and laboratory settings. The nitro compounds formed are important intermediates for the synthesis of amines, dyes, pharmaceuticals, and explosives like TNT (Trinitrotoluene).

Key Points:

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  Nitration introduces a –NO₂ group.

  
  


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  Reagents: conc. HNO₃ and conc. H₂SO₄.

  
  


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  Reaction type: Electrophilic substitution.

  
  


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  Common products: Nitrobenzene, nitrotoluene, nitrophenol.

  
  

Therefore, the introduction of a nitro group (–NO₂) into an organic compound is known as nitration.

✅ Correct Option: A) Nitration