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.
This question appeared on the ETEA MDCAT 2014 paper, which you can sit online with every answer explained.
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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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