Question

Select the most reactive and least reactive compound from the following, towards nitration. Benzene, Chlorobenzene, nitrobenzene, Toluene.

Answer 1

• When nitro group reacts with these compounds, they undergo electrophilic aromatic substitution reaction (EAS) i.e. nitration reaction.
  
• In this reaction, the benzene needs to donate electrons to the nitro group from the ring.
  
• Benzene becomes less reactive towards EAS reaction when deactivating groups are present on it. Generally, deactivating groups are electron withdrawing groups.
  
• Now,
  

methyl group in Toluene donates an electron to the benzene ring by hyperconjugation thus it weakly rings activating group and electron donating group.

• The $-Cl$ group in chlorobenzene is $\pi$ electron donor group but it is also an electron withdrawing group. Thus it slightly deactivates the ring.
  
• Now, nitro group in nitrobenzene is electron withdrawing group. Thus it strongly deactivates the ring.
  
• Thus, the decreasing order of the group towards nitration reaction can be given as:
  

$Toluene>Chlorobenzene>Benzene>Nitrobenzene$