Asked in UHS MDCAT 2018 2018Moderate

Which of the following acts as an electrophile in the electrophilic substitution of benzene with bromine?

Correct answer: A. Br+

  • A. Br+
  • B. FeCl4+
  • C. Fe2+
  • D. Fe3+

Explanation

Benzene reacts with bromine in an electrophilic substitution reaction, but only in the presence of a catalyst to yield bromobenzene. As a bromine molecule approaches the benzene ring, the delocalised electrons in the ring repel electrons in the bromine-bromine bond. It is the slightly positive end of the bromine molecule which acts as the electrophile. The presence of the aluminium chloride helps this polarisation.

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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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