Asked in ETEA MDCAT 2014 2014Moderate

Which of the following substitutents is an Ortho and Para director and ring deactivating?

Correct answer: C. -Cl

  • A. -OH
  • B. -NH2
  • C. -Cl
  • D. -OCH3

Explanation

In electrophilic aromatic substitution, the nature of the substituent on the benzene ring plays a crucial role in determining the position of new substituents and the reactivity of the ring. Ortho-para directors are groups that direct incoming electrophiles to the 2, 4 (ortho, para) positions. While most ortho-para directors are activating, -Cl is an exception as it directs due to resonance but deactivates due to a strong inductive effect. This means it reduces the overall reactivity of the benzene ring but still allows for substitution at ortho and para positions.In contrast, -OH and -NH2 groups are strong activators, and -OCH3 is moderately activating; all increase the reactivity of the benzene ring and direct electrophiles to ortho and para positions without deactivating the ring.

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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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