Moderate

During sulphonation of benzene H2SO4 generates the electrophile _________________?

Correct answer: C. SO3

  • A. HSO4-
  • B. SO2
  • C. SO3
  • D. H+

Explanation

In concentrated sulfuric acid or oleum, sulfur trioxide, SO3, acts as the electrophile that attacks the benzene ring during sulphonation. H+ helps generate the reactive medium but is not the electrophile that introduces the sulfonic group, so students may choose H+ by focusing on the acid catalyst.

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About Benzene and Aromatic Compounds

Benzene has a planar ring of delocalised π electrons, giving aromatic stability and equal carbon-carbon bond lengths. The topic covers resonance, electrophilic substitution reactions such as nitration, halogenation, sulphonation and Friedel-Crafts reactions, along with substituent effects and the distinction between substitution in benzene and addition in ordinary alkenes.

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