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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4:08 minutes

Problem 42

Textbook Question

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

Verified step by step guidance

Step 1: Identify the radicals provided in the image. These include: methyl radical (•CH₃), ethyl radical (CH₃CH₂•), benzyl radical (C₆H₅CH₂•), tertiary butyl radical ((CH₃)₃C•), isopropyl radical ((CH₃)₂CH•), and allyl radical (CH₂=CH—CH₂•).

Step 2: Recall the factors that influence radical stability. Stability is determined by resonance stabilization, hyperconjugation, and inductive effects. Radicals that are resonance-stabilized are generally more stable than those stabilized by hyperconjugation or inductive effects.

Step 3: Analyze each radical for resonance stabilization. The benzyl radical (C₆H₅CH₂•) and allyl radical (CH₂=CH—CH₂•) are resonance-stabilized, making them more stable than the others. Benzyl radical has extensive resonance due to the aromatic ring, while allyl radical has resonance across the π-bond.

Step 4: Consider hyperconjugation and inductive effects for the remaining radicals. The tertiary butyl radical ((CH₃)₃C•) is highly stabilized by hyperconjugation due to the presence of three methyl groups. The isopropyl radical ((CH₃)₂CH•) is next, followed by the ethyl radical (CH₃CH₂•), and finally the methyl radical (•CH₃), which has no hyperconjugation or resonance stabilization.

Step 5: Rank the radicals in decreasing order of stability based on the analysis: Benzyl radical (C₆H₅CH₂•) > Allyl radical (CH₂=CH—CH₂•) > Tertiary butyl radical ((CH₃)₃C•) > Isopropyl radical ((CH₃)₂CH•) > Ethyl radical (CH₃CH₂•) > Methyl radical (•CH₃).

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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 free radicals, which are species with unpaired electrons. The stability of a radical is influenced by factors such as the degree of substitution (primary, secondary, tertiary) and resonance effects. Tertiary radicals are generally more stable than secondary, which are more stable than primary, due to hyperconjugation and the ability to delocalize the unpaired electron.

Hyperconjugation

Hyperconjugation is a stabilizing interaction that occurs when the electrons in a sigma bond (C-H or C-C) interact with an adjacent empty p-orbital or a radical. This effect allows for the delocalization of the unpaired electron in radicals, enhancing their stability. The more alkyl groups attached to the carbon bearing the radical, the greater the hyperconjugation, leading to increased stability.

Resonance

Resonance is a concept in organic chemistry where a molecule can be represented by two or more valid Lewis structures, known as resonance structures. In the case of radicals, resonance can significantly enhance stability by allowing the unpaired electron to be delocalized over multiple atoms. For example, benzyl radicals benefit from resonance, making them more stable than non-resonance-stabilized radicals.

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Textbook Question

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

(d)

Textbook Question

Methyl t-butyl ether (MTBE) is used preferentially over diethyl ether because it is less prone to form peroxides. Explain this observation in terms of the two structures.

Textbook Question

a. Which of the hydrogens in the structure in the margin is the easiest for a chlorine radical to remove?

b. How many secondary hydrogens does the structure have?

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

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

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.

Textbook Question

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

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