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

Free Radical Halogenation

Organic Chemistry

11. Radical Reactions

Free Radical Halogenation

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4:24 minutes

Problem 57

Textbook Question

Other molecules can be used as initiators in radical reactions. One such molecule is 2, 2'-azobisisobutyronitrile (AIBN). Show an arrow-pushing mechanism that rationalizes the formation of the following radical species. What are the driving forces of this reaction?

Verified step by step guidance

Identify the structure of 2,2'-azobisisobutyronitrile (AIBN) and note the azo group (N=N) in the center of the molecule. This group is key to the radical formation.

Understand that the reaction is initiated by heat, which provides the energy needed to break the N=N bond homolytically, resulting in the formation of two radicals.

Use arrow-pushing to show the homolytic cleavage of the N=N bond. Draw arrows starting from the bond and pointing towards each nitrogen atom, indicating the movement of one electron to each nitrogen.

Recognize that the driving force of this reaction is the formation of nitrogen gas (N₂), which is a very stable molecule. The release of N₂ gas provides a thermodynamic push for the reaction to proceed.

Illustrate the final step where the nitrogen radicals are released as nitrogen gas, and the remaining carbon-centered radicals are formed. These radicals can then participate in further radical reactions.

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Key Concepts

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

Radical Reactions

Radical reactions involve species with unpaired electrons, known as radicals, which are highly reactive. These reactions typically proceed through three main steps: initiation, propagation, and termination. Understanding how radicals form and react is crucial for analyzing mechanisms, such as those involving AIBN, which generates radicals that can initiate polymerization or other reactions.

Arrow-Pushing Mechanism

The arrow-pushing mechanism is a method used to depict the movement of electrons during chemical reactions. Arrows indicate the direction of electron flow, helping to visualize bond formation and breaking. This technique is essential for illustrating the steps in radical reactions, allowing students to understand how intermediates are formed and how the overall reaction progresses.

Driving Forces of Reactions

Driving forces in chemical reactions refer to the factors that favor the progression of a reaction towards products. These can include thermodynamic stability, such as the formation of stable products or the release of energy (exothermic reactions). In radical reactions, the formation of stable radical intermediates and the overall decrease in energy can serve as significant driving forces, influencing the reaction pathway and outcome.

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Related Practice

Textbook Question

We have studied the following reactions in previous chapters. For each, (i) indicate which reaction sheets they should appear on, (ii) show the best structure to use to represent them, and (iii) write the notes you could put in the margin so that the mechanism is implied.

(b) Radical halogenation of an alkane

Textbook Question

Provide a mechanism for the chlorination of cyclohexane. Be sure to include initiation, propagation, and three possible termination steps.

Textbook Question

For the following reaction, answer questions (a)–(d).

(a) Give an arrow-pushing mechanism, including the initiation step and two propagation steps.

Textbook Question

Predict the major products of the following alkane halogenation reactions. [The number of products shown ignores the formation of racemic mixtures.]

(c)

Textbook Question

Cyclizations can be carried out under radical conditions involving Bu₃SnH and a catalytic amount of AIBN. Suggest a mechanism for this reaction. [Pay close attention to the bonds formed and broken in developing your mechanism. It may be helpful to number the carbons.]

Textbook Question

What alkane, with molecular formula C₅H₁₂, forms only one monochlorinated product when it is heated with Cl₂?

Textbook Question

Explain why the rate of bromination of methane decreases if HBr is added to the reaction mixture.

Textbook Question

How many alkyl halides are obtained from monochlorination of the alkanes in Problem 4 if stereoisomers are included?

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