Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

19. Reactions of Aromatics: EAS and Beyond

EAS:Halogenation Mechanism

Organic Chemistry

19. Reactions of Aromatics: EAS and Beyond

EAS:Halogenation Mechanism

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Problem 75

Textbook Question

Bromination of phenol or aniline does not require the use of a Lewis acid catalyst and often results in trihalogenation. Why?

Verified step by step guidance

Identify the functional groups present in phenol and aniline. Phenol has a hydroxyl group (-OH) attached to the benzene ring, and aniline has an amino group (-NH2) attached to the benzene ring.

Understand the activating effects of these functional groups. Both the hydroxyl group in phenol and the amino group in aniline are strong electron-donating groups. They increase the electron density on the benzene ring through resonance, making the ring more reactive towards electrophilic aromatic substitution.

Recognize the role of electron-donating groups in directing substitution. The -OH and -NH2 groups are ortho/para-directing, meaning they increase the likelihood of substitution occurring at the ortho and para positions relative to the functional group.

Explain why a Lewis acid catalyst is not required. The increased electron density on the benzene ring due to the electron-donating groups makes the ring sufficiently reactive to undergo bromination without the need for a Lewis acid catalyst, which is typically used to activate the bromine.

Discuss why trihalogenation occurs. The high reactivity of the benzene ring in phenol and aniline, due to the strong activating effects of the -OH and -NH2 groups, often leads to multiple brominations, resulting in trihalogenation at the ortho and para positions.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electrophilic Aromatic Substitution

Electrophilic aromatic substitution (EAS) is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. In the case of phenol and aniline, the hydroxyl (-OH) and amino (-NH2) groups are strong activating groups that enhance the reactivity of the aromatic ring, allowing for multiple substitutions without the need for a Lewis acid catalyst.

Activating Groups

Activating groups are substituents on an aromatic ring that increase the rate of electrophilic substitution reactions. Hydroxyl and amino groups are examples of activating groups that donate electron density to the ring, making it more nucleophilic. This increased reactivity facilitates the bromination process, often leading to trihalogenation due to the enhanced electrophilic attack on the ring.

Trihalogenation

Trihalogenation refers to the substitution of three halogen atoms in a compound. In the context of phenol and aniline, the presence of strong activating groups allows for multiple bromine atoms to be introduced onto the aromatic ring. This occurs because the electron-rich nature of the ring can stabilize the positive charge that develops during the electrophilic substitution, enabling further substitutions to occur.

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What is the major product(s) of each of the following reactions?

a. bromination of p-methylbenzoic acid

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What products are obtained from the reaction of the following compounds with one equivalent of Br₂, using FeBr₃ as a catalyst?

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What is the major product(s) of each of the following reactions?

b. chlorination of o-benzenedicarboxylic acid

Textbook Question

Why isn’t FeBr₃ used as a catalyst in the first step of the synthesis of 1,3,5-tribromobenzene?

Multiple Choice

Predict the major, organic product for the following reaction.

Textbook Question

The following are all substitution reactions, two of which we study in later chapters. With no knowledge of mechanism, what would you expect the ratio of products to be for each reaction, based on a random statistical distribution?

(b) Replacing a hydrogen (H) with bromine (Br):

Textbook Question

Propose a mechanism for the aluminum chloride–catalyzed reaction of benzene with chlorine.

Textbook Question

Styrene (vinylbenzene) undergoes electrophilic aromatic substitution much faster than benzene, and the products are found to be primarily ortho- and para-substituted styrenes. Use resonance forms of the intermediates to explain these results.

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