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

Radical Stability

Organic Chemistry

11. Radical Reactions

Radical Stability

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6:26 minutes

Problem 59b

Textbook Question

A student adds NBS to a solution of 1-methylcyclohexene and irradiates the mixture with a sunlamp until all the NBS has reacted. After a careful distillation, the product mixture contains two major products of formula C₇H₁₁Br.
b. Rank these three intermediates from most stable to least stable.

Verified step by step guidance

Identify the reaction type: The reaction involves NBS (N-Bromosuccinimide) and light (hv), which indicates an allylic bromination reaction. This reaction selectively brominates the allylic position of alkenes.

Determine the possible allylic positions: In 1-methylcyclohexene, the double bond is between two carbons in the cyclohexene ring. The allylic positions are the carbons adjacent to the double bond. Analyze the structure to identify all possible allylic carbons.

Generate the allylic radicals: When the reaction occurs, the bromine radical abstracts a hydrogen atom from the allylic positions, forming allylic radicals. Draw the possible allylic radicals and consider resonance structures to determine their stability.

Rank the stability of the intermediates: The stability of allylic radicals depends on resonance delocalization and the degree of substitution. More substituted radicals and those with greater resonance stabilization are more stable. Rank the radicals based on these criteria.

Conclude the ranking: Based on the analysis, rank the three intermediates (allylic radicals) from most stable to least stable. This ranking will help explain the major products observed in the reaction.

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Key Concepts

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

Radical Stability

Radical stability refers to the relative stability of radical intermediates formed during reactions. Factors influencing stability include the degree of substitution (tertiary radicals are more stable than secondary, which are more stable than primary) and resonance effects. In the context of the reaction with NBS, understanding the stability of the radical intermediates is crucial for predicting the major products formed.

Electrophilic Addition Reactions

Electrophilic addition reactions involve the addition of an electrophile to a nucleophile, typically across a double bond. In this case, NBS acts as an electrophile, adding bromine to the alkene (1-methylcyclohexene). Recognizing the mechanism of this addition helps in understanding the formation of the products and the intermediates involved in the reaction.

Distillation and Product Separation

Distillation is a separation technique used to purify liquids based on differences in boiling points. After the reaction, distillation is employed to isolate the products from unreacted materials and byproducts. Understanding the principles of distillation is essential for analyzing the resulting product mixture and determining the composition of the major products formed in the reaction.

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Related Practice

Textbook Question

Rank the following radicals in decreasing order of stability. Classify each as primary, secondary, or tertiary.

a. The isopentyl radical,

b. The 3-methyl-2-butyl radical,

c. The 2-methyl-2-butyl radical,

Textbook Question

Use the information in Table 4-2 (p. 167) to rank the following radicals in decreasing order of stability.

Textbook Question

For each set of reactive intermediates, rank them in order of reactivity (1 = most reactive).

(b)

Textbook Question

Use the information in Table 4-2 to explain why toluene (PhCH₃) has a very high octane rating of 111. Write an equation to show how toluene reacts with an alkyl free radical to give a relatively stable radical.

Textbook Question

Explain the dramatic difference in rotational energy barriers of the following three alkenes. (Hint: Consider what the transition states must look like.)

Textbook Question

The following ethers are ranked according to their ability to form explosive peroxides. Explain this ranking based on your knowledge of the reaction mechanism.

Textbook Question

Based on the stability of the radicals produced, predict which bond in each pair would have the higher bond-dissociation energy.

(a)

Textbook Question

Based on the stability of the radicals produced, predict which bond in each pair would have the higher bond-dissociation energy.

(b)

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