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

Calculating Radical Yields

Organic Chemistry

11. Radical Reactions

Calculating Radical Yields

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6:18 minutes

Problem 45

Textbook Question

At 600 °C, the ratio of the relative rates of formation of a tertiary, a secondary, and a primary radical by a chlorine radical is 2.6 : 2.1 : 1. Explain the change in the degree of regioselectivity compared to what was found in Problem 44.

Verified step by step guidance

Understand the context: The problem involves the regioselectivity of radical formation during a chlorination reaction. Chlorine radicals are less selective than bromine radicals, and the regioselectivity depends on the relative stability of the radicals formed (tertiary > secondary > primary). The given ratio (2.6 : 2.1 : 1) reflects the relative rates of radical formation at 600 °C.

Recall the concept of regioselectivity: Regioselectivity refers to the preference for forming one constitutional isomer over another. In this case, the preference is based on the stability of the radicals formed. Tertiary radicals are the most stable due to hyperconjugation and inductive effects, followed by secondary and then primary radicals.

Compare with Problem 44: In Problem 44, the regioselectivity might have been different (likely higher) because the temperature or halogen used (e.g., bromine) could have influenced the selectivity. Higher temperatures, as in this problem (600 °C), reduce regioselectivity because the reaction becomes more kinetically controlled, and the energy difference between forming different radicals becomes less significant.

Explain the effect of temperature: At higher temperatures, the energy barrier for radical formation is more easily overcome, and the reaction becomes less selective. This is why the ratio of 2.6 : 2.1 : 1 shows a smaller difference between the rates of tertiary, secondary, and primary radical formation compared to what might have been observed at lower temperatures or with bromine radicals.

Summarize the change in regioselectivity: The degree of regioselectivity decreases at higher temperatures because the reaction becomes less dependent on the stability of the radicals and more dependent on the kinetic factors. This explains why the ratio of radical formation rates is closer together (2.6 : 2.1 : 1) compared to the likely higher regioselectivity in Problem 44.

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Key Concepts

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

Radical Stability

The stability of radicals is crucial in organic chemistry, as it influences their reactivity and formation rates. Tertiary radicals are more stable than secondary and primary radicals due to hyperconjugation and inductive effects from surrounding alkyl groups. This stability hierarchy explains why tertiary radicals are formed preferentially in reactions involving radical mechanisms.

Regioselectivity

Regioselectivity refers to the preference of a chemical reaction to occur at one site over another in a molecule. In radical reactions, the regioselectivity can shift based on the stability of the resulting radicals. The observed ratio of radical formation indicates that the reaction conditions, such as temperature, can significantly influence which radicals are favored.

Temperature Effects on Reaction Rates

Temperature plays a vital role in chemical reactions, affecting the kinetic energy of molecules and the rates of reaction. At higher temperatures, the increased energy can lead to a greater formation of radicals and can alter the selectivity of the reaction. In this case, the elevated temperature of 600 °C likely enhances the formation of more stable tertiary radicals, thus changing the regioselectivity compared to lower temperature conditions.

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Suppose you intend to synthesize the secondary alkyl halide from each reaction shown.

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Predict whether chlorination or bromination would have a greater deuterium kinetic isotope effect.

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Predict the product(s) of the following halogenation reactions. Only one equivalent of the halogen is used in each case. If the reaction proceeds selectively, indicate this by only drawing the major product. If the reaction is not selective, draw all possible products.

(b)

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Suppose a 2-halobutane was needed for a synthetic sequence. Starting your synthesis with butane, would it be best to put a chlorine or bromine at that position? Explain.

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Multiple Choice

What is the percentage yield of the major product?

Textbook Question

The chlorination of pentane gives a mixture of three monochlorinated products.

b. Predict the ratios in which these monochlorination products will be formed, remembering that a chlorine atom abstracts a secondary hydrogen about 4.5 times as fast as it abstracts a primary hydrogen.

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Given the ratio of products obtained in the bromination of propane, calculate the relative reactivity of a 1° C–H bond to a 2° C–H bond under these conditions.

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