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

Anti Markovnikov Addition of Br

Organic Chemistry

11. Radical Reactions

Anti Markovnikov Addition of Br

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5:50 minutes

Problem 13

Textbook Question

Write the propagation steps for the addition of HBr to 1-methylcyclohexene in the presence of a peroxide

Verified step by step guidance

Identify the reaction mechanism: The presence of a peroxide indicates that the reaction proceeds via a free radical mechanism (anti-Markovnikov addition) rather than the typical electrophilic addition mechanism.

Initiate the reaction: The peroxide decomposes to form two alkoxy radicals (RO•) under heat or light. These radicals are responsible for initiating the free radical chain reaction.

Step 1 of propagation: The alkoxy radical (RO•) abstracts a hydrogen atom from HBr, forming a bromine radical (Br•) and an alcohol (ROH). This step generates the reactive species needed for the next step.

Step 2 of propagation: The bromine radical (Br•) reacts with 1-methylcyclohexene. The Br• adds to the less substituted carbon of the double bond (anti-Markovnikov addition), forming a more stable secondary radical intermediate.

Step 3 of propagation: The secondary radical intermediate reacts with another molecule of HBr, abstracting a hydrogen atom to form the final product (1-bromo-2-methylcyclohexane) and regenerating the bromine radical (Br•), which continues the chain reaction.

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Key Concepts

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

Electrophilic Addition

Electrophilic addition is a fundamental reaction mechanism in organic chemistry where an electrophile reacts with a nucleophile, typically involving alkenes. In the case of HBr addition to alkenes, the double bond acts as a nucleophile, attacking the electrophilic hydrogen atom of HBr, leading to the formation of a carbocation intermediate.

Peroxide Effect (Anti-Markovnikov Addition)

The peroxide effect refers to the phenomenon where the addition of HBr to alkenes in the presence of peroxides leads to anti-Markovnikov addition. This means that the bromine atom attaches to the less substituted carbon of the alkene, contrary to the usual Markovnikov rule, due to the formation of free radicals instead of carbocations during the reaction.

Free Radical Mechanism

The free radical mechanism involves a series of steps including initiation, propagation, and termination, where free radicals are generated and react to form products. In the context of HBr addition to 1-methylcyclohexene with peroxides, the initiation step generates free radicals that facilitate the addition of HBr in a way that favors the formation of the less substituted product.

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Related Practice

Textbook Question

Provide the mechanism of the radical reactions shown.

(a)

Textbook Question

What alkyl halide will be obtained in greatest yield? Ignore stereoisomers.

Textbook Question

What alkyl halide will be obtained in greatest yield? Ignore stereoisomers.

Textbook Question

What five-carbon alkene forms the same product whether it reacts with HBr in the presence of a peroxide or with HBr in the absence of a peroxide?

Textbook Question

Predict the major products of the following alkene halogenation reactions. [D is the symbol for deuterium, an isotope of hydrogen.]

(a)

Textbook Question

Predict the major products of the following alkene halogenation reactions. [D is the symbol for deuterium, an isotope of hydrogen.]

(b)

Textbook Question

Provide the expected product for the reaction of each of the following alkenes with (i) HBr and (ii) HBr, H₂O₂.

(e)

Textbook Question

Which reagent system (HBr or HBr, H₂O₂) would you use to carry out the following transformations?

(c)

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