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

Previous problemNext problem

5:26 minutes

Problem 33

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.

Verified step by step guidance

Begin by identifying the allylic halide structure. Allylic halides have a halogen atom attached to a carbon atom that is adjacent to a carbon-carbon double bond.

Recognize that the reaction is under thermodynamic control, meaning the most stable product is favored. This implies that the reaction can equilibrate between different allylic halides.

Consider the mechanism of allylic rearrangement. The key step involves the reversible formation of a π-allyl radical or cation intermediate, which allows for the migration of the halide.

Use arrow-pushing to illustrate the formation of the π-allyl intermediate. Start by showing the homolytic cleavage of the C-X bond, where X is the halogen, to form a radical or cation at the allylic position.

Show the rearrangement of the π-allyl intermediate to form the more stable allylic halide. This involves the movement of the double bond and the reformation of the C-X bond at a different position, resulting in the more stable alkene configuration.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

Key Concepts

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

Allylic Halogenation

Allylic halogenation is a reaction where a halogen atom is introduced at the allylic position of an alkene, which is the carbon atom adjacent to a double bond. This reaction often involves radical intermediates and is significant because it can lead to the formation of more stable alkenes through rearrangement or resonance stabilization.

Thermodynamic Control

Thermodynamic control in a chemical reaction refers to conditions where the product distribution is determined by the relative stability of the products. Under these conditions, the reaction is reversible, and the most stable product predominates, as it is the lowest energy state. This contrasts with kinetic control, where the fastest-forming product is favored.

Arrow-Pushing Mechanism

Arrow-pushing is a technique used in organic chemistry to illustrate the movement of electrons during chemical reactions. It involves using curved arrows to show how electron pairs move from nucleophiles to electrophiles, helping to visualize the step-by-step process of bond formation and breaking. In the context of allylic halogenation, it helps explain how less stable intermediates can rearrange to form more stable products.

Watch next

Master The general mechanism of Allylic Halogenation. with a bite sized video explanation from Johnny

Start learning

Related Videos

Related Practice

Textbook Question

Predict the products of the following allylic halogenation reactions.

(d)

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

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

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?

Show more practices

Download the Mobile app

Privacy

Do not sell my personal information

Accessibility

Patent notice

Sitemap