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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6:14 minutes

Problem 35

Textbook Question

The deuterium kinetic isotope effect for the halogenation of an alkane is defined in the following equation, where X･ = Cl･ or Br･

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

Verified step by step guidance

Step 1: Understand the concept of the deuterium kinetic isotope effect. It is a measure of the difference in reaction rates between the cleavage of a C-H bond and a C-D bond. The heavier isotope (deuterium) forms stronger bonds, which require more energy to break compared to the lighter isotope (hydrogen).

Step 2: Analyze the halogenation process. Halogenation involves the homolytic cleavage of the C-H or C-D bond by a halogen radical (X•, where X = Cl or Br). The rate of bond cleavage depends on the bond dissociation energy and the reactivity of the halogen radical.

Step 3: Compare the reactivity of chlorine and bromine radicals. Chlorine radicals (Cl•) are more reactive than bromine radicals (Br•) due to their higher electronegativity and smaller size, which allows them to interact more effectively with the C-H or C-D bond.

Step 4: Consider the bond dissociation energy. The C-H bond has a lower bond dissociation energy compared to the C-D bond, making it easier to cleave. Since chlorine radicals are more reactive, they will exhibit a greater difference in the cleavage rates of C-H and C-D bonds, leading to a larger deuterium kinetic isotope effect.

Step 5: Predict the outcome. Based on the higher reactivity of chlorine radicals and the stronger C-D bond, chlorination is expected to have a greater deuterium kinetic isotope effect compared to bromination.

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Key Concepts

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

Kinetic Isotope Effect (KIE)

The kinetic isotope effect refers to the change in reaction rate that occurs when one atom in a molecule is replaced by one of its isotopes. In organic reactions, this effect is particularly significant for hydrogen isotopes, such as deuterium, which is heavier than protium. The KIE can provide insights into the transition state of a reaction, as heavier isotopes typically lead to slower reaction rates due to their increased mass.

Halogenation of Alkanes

Halogenation is a substitution reaction where a halogen atom (like chlorine or bromine) replaces a hydrogen atom in an alkane. This process typically involves radical mechanisms, where halogen radicals react with alkanes to form alkyl halides. The nature of the halogen affects the reaction's kinetics and the stability of the transition state, which is crucial for understanding the KIE in this context.

Radical Stability

Radical stability is a key factor in determining the reactivity of halogen radicals during the halogenation of alkanes. Bromine radicals are generally more stable than chlorine radicals due to their larger size and lower bond dissociation energy. This stability influences the rate of reaction and the extent of the kinetic isotope effect, as more stable radicals lead to a more favorable transition state, impacting the overall reaction kinetics.

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Related Practice

Textbook Question

The following are all substitution reactions, two of which we study in later chapters. With no knowledge of mechanism, what would you expect the ratio of products to be for each reaction, based on a random statistical distribution?

(a) Replacing a hydrogen (H) with chlorine (Cl):

Textbook Question

What would be the product ratio in the chlorination of propane if all the hydrogens were abstracted at equal rates?

Textbook Question

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

(a) What is the atom economy of each reaction?

Textbook Question

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

(b) What is the E-factor, effective mass yield, and process mass intensity?

Textbook Question

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)

Textbook Question

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.

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.

Multiple Choice

What is the percentage yield of the major product?

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The deuterium kinetic isotope effect for the halogenation of an alkane is defined in the following equation, where X･ = Cl･ or Br･Predict whether chlorination or bromination would have a greater deuterium kinetic isotope effect.

Key Concepts

Kinetic Isotope Effect (KIE)

Halogenation of Alkanes

Radical Stability

Watch next

The deuterium kinetic isotope effect for the halogenation of an alkane is defined in the following equation, where X･ = Cl･ or Br･

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