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

Side-Chain Halogenation

Organic Chemistry

19. Reactions of Aromatics: EAS and Beyond

Side-Chain Halogenation

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4:13 minutes

Problem 31c

Textbook Question

What is the major product of the following reactions? Disregard stereoisomers:
c.

Verified step by step guidance

Step 1: Recognize the reagent and reaction type. NBS (N-Bromosuccinimide) in the presence of heat (Δ) and peroxide is commonly used for allylic or benzylic bromination. This reaction selectively replaces a hydrogen atom at the allylic or benzylic position with a bromine atom.

Step 2: Identify the benzylic position in the given molecule. The structure contains a benzene ring with an isopropyl group attached. The benzylic position is the carbon directly attached to the benzene ring within the isopropyl group.

Step 3: Determine the stability of the radical intermediate. The benzylic radical formed during the reaction is highly stabilized due to resonance with the aromatic ring. This stabilization makes the benzylic position the preferred site for bromination.

Step 4: Predict the product. The bromine atom will replace one of the hydrogens at the benzylic position, resulting in the formation of a brominated product at this site.

Step 5: Disregard stereoisomers. Since the problem specifies to disregard stereoisomers, focus only on the major product formed at the benzylic position without considering stereochemical variations.

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Key Concepts

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

Side-Chain Halogenation

Side-chain halogenation is a reaction where a halogen atom replaces a hydrogen atom in the side chain of an organic molecule. This process typically involves the use of reagents like N-bromosuccinimide (NBS) in the presence of heat or light, which facilitates the formation of a radical intermediate. The reaction is selective for the most stable radical, leading to the formation of the major product.

Radical Mechanism

The radical mechanism involves the formation and reaction of free radicals, which are highly reactive species with unpaired electrons. In the context of halogenation, the reaction proceeds through three main steps: initiation, propagation, and termination. The initiation step generates radicals, the propagation step involves the reaction of these radicals with the substrate, and the termination step leads to the recombination of radicals.

NBS and Peroxide

N-bromosuccinimide (NBS) is a reagent commonly used for bromination reactions, particularly in the presence of peroxides. Peroxides facilitate the formation of bromine radicals from NBS under heat, promoting the radical halogenation process. This method is advantageous as it allows for selective bromination at the allylic or benzylic positions, which is crucial for determining the major product in the reaction.

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Related Practice

Textbook Question

For each compound, predict the major product of free-radical bromination. Remember that bromination is highly selective, and only the most stable radical will be formed.

(e)

Textbook Question

(c) Based on what you know about the relative stabilities of alkyl radicals and benzylic radicals, predict the product of addition of HBr to 1-phenylpropene in the presence of a free-radical initiator.

(d) Propose a mechanism for this reaction.

Textbook Question

Suggest reagents and reaction conditions that would result in synthesis of the following bromoalkanes.

(c)

Textbook Question

Predict the product of the following benzylic bromination reactions.

(c)

Textbook Question

Show how you would convert (in one or two steps) 1-phenylpropane to the three products shown below. In each case, explain what unwanted reactions might produce undesirable impurities in the product.

Textbook Question

Show the products you expect when each compound reacts with NBS with light shining on the reaction.

(d)

Textbook Question

Predict the major products of treating the following compounds with hot, concentrated potassium permanganate, followed by acidification with dilute HCl.

(a) isopropylbenzene

(b) p-xylene

(c)

Textbook Question

Predict the product of the following benzylic bromination reactions.

(a)

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