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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1:45 minutes

Problem 28

Textbook Question

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

Verified step by step guidance

Understand the role of FeBr₃ in electrophilic aromatic substitution (EAS): FeBr₃ is a Lewis acid catalyst that activates Br₂ by polarizing the Br-Br bond, making one bromine atom more electrophilic and reactive toward the aromatic ring.

Recognize the reactivity of benzene: Benzene is relatively stable due to its aromaticity, and FeBr₃ is typically used to facilitate the bromination of benzene by generating a stronger electrophile (Br⁺).

Consider the product, 1,3,5-tribromobenzene: This compound has three bromine substituents in a symmetrical arrangement. Bromine atoms are electron-withdrawing and deactivating, making the benzene ring less reactive after each bromination step.

Analyze the first bromination step: In the synthesis of 1,3,5-tribromobenzene, the first bromination does not require FeBr₃ because benzene is sufficiently reactive to undergo bromination with Br₂ alone. Using FeBr₃ in the first step could lead to over-bromination or undesired side reactions.

Conclude why FeBr₃ is not used initially: FeBr₃ is unnecessary in the first step because benzene's reactivity is adequate for bromination with Br₂. The catalyst is more useful in subsequent steps when the ring becomes less reactive due to the electron-withdrawing effects of the bromine substituents.

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Key Concepts

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

Electrophilic Aromatic Substitution (EAS)

Electrophilic Aromatic Substitution is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. This process is crucial for synthesizing substituted aromatic compounds, such as 1,3,5-tribromobenzene. Understanding the mechanism of EAS helps in predicting the reactivity and orientation of substituents on the aromatic ring.

Catalysts in Organic Reactions

Catalysts are substances that increase the rate of a chemical reaction without being consumed in the process. In organic reactions, catalysts can help stabilize transition states or lower activation energy. The choice of catalyst is critical, as it must facilitate the desired reaction while avoiding side reactions or deactivation, which is relevant in the context of using FeBr3.

Reactivity of Iron(III) Bromide (FeBr3)

Iron(III) bromide (FeBr3) is often used as a Lewis acid catalyst in electrophilic aromatic substitution reactions. However, its reactivity can be influenced by the nature of the electrophile and the substrate. In the case of synthesizing 1,3,5-tribromobenzene, FeBr3 may not be suitable due to potential side reactions or insufficient activation of the bromine electrophile, leading to poor yields.

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Related Practice

Textbook Question

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

Textbook Question

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

a. bromination of p-methylbenzoic acid

Textbook Question

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

Textbook Question

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

b. chlorination of o-benzenedicarboxylic acid

Textbook Question

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

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.

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