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

11. Radical Reactions

Allylic Bromination

Organic Chemistry

11. Radical Reactions

Allylic Bromination

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5:58 minutes

Problem 46c

Textbook Question

Draw the products of the following reactions, including all stereoisomers:
c.

Verified step by step guidance

Identify the type of reaction: The presence of NBS (N-bromosuccinimide) and peroxide indicates a radical bromination reaction, specifically allylic bromination.

Recognize the allylic position: In the given alkene, the allylic position is the carbon adjacent to the double bond. This is where the bromine will be added.

Initiate the radical mechanism: Peroxide initiates the formation of bromine radicals. The heat (Δ) helps in the homolytic cleavage of the peroxide bond, generating radicals.

Form the allylic radical: The bromine radical abstracts a hydrogen from the allylic position, forming an allylic radical. This radical is stabilized by resonance.

Add bromine to the allylic radical: The bromine radical reacts with the allylic radical, forming the allylic bromide. Consider all possible resonance structures to identify all stereoisomers.

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Key Concepts

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

NBS (N-Bromosuccinimide)

NBS is a reagent commonly used in organic chemistry for bromination reactions, particularly in allylic and benzylic positions. It provides a source of bromine in a controlled manner, allowing for selective substitution reactions. The presence of NBS in the reaction facilitates the formation of radical intermediates, which are crucial for the subsequent steps in the reaction mechanism.

Radical Mechanism

The radical mechanism involves the formation of free radicals, which are highly reactive species with unpaired electrons. In the context of the reaction with NBS, the radical mechanism typically proceeds through initiation, propagation, and termination steps. This mechanism is essential for understanding how bromine is added to the allylic position of the alkene, leading to the formation of various products, including stereoisomers.

Stereoisomerism

Stereoisomerism refers to the phenomenon where compounds have the same molecular formula and connectivity but differ in the spatial arrangement of atoms. In reactions involving alkenes and radicals, stereoisomers can arise due to the formation of chiral centers or the presence of double bonds. Understanding stereoisomerism is crucial for predicting the different products formed in the reaction, including cis/trans or E/Z isomers.

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Related Practice

Textbook Question

In the following allylic radicals, identify the carbon where the new C–Br bond is most likely to form in the second propagation step.

(a)

Textbook Question

In the presence of a small amount of bromine, cyclohexene undergoes the following light-promoted reaction:

d. Explain why cyclohexene reacts with bromine much faster than cyclohexane, which must be heated to react.

Textbook Question

In the presence of a small amount of bromine, the following light-promoted reaction has been observed.

a. Write a mechanism for this reaction. Your mechanism should explain how both products are formed. (Hint: Notice which H atom has been lost in both products.)

Textbook Question

The fact that allylic halogenation results in formation of the most stable alkene suggests that it is under thermodynamic control. Thus, the second propagation step must be reversible. Suggest an arrow-pushing mechanism by which the less stable allylic halide might equilibrate to the more stable allylic halide.

Textbook Question

The halogenation of an alkane when there is an alkene present in the molecule does not proceed with the regioselectivity you might expect. Using principles similar to those developed in this chapter, rationalize the formation of A as the only product. We study this reaction further in Chapter 8.

Multiple Choice

Predict the major, organic product of the following reaction.

Multiple Choice

Which reaction is best suited to form the following product?

Textbook Question

The light-initiated reaction of 2,3-dimethylbut-2-ene with N-bromosuccinimide (NBS) gives two products:

a. Give a mechanism for this reaction, showing how the two products arise as a consequence of the resonance-stabilized intermediate.

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