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

6. Thermodynamics and Kinetics

Enthalpy

Organic Chemistry

6. Thermodynamics and Kinetics

Enthalpy

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2:38 minutes

Problem 39

Textbook Question

Give the approximate bond-dissociation energy for each indicated bond.

Verified step by step guidance

Identify the bonds in question for which the bond-dissociation energy (BDE) is required. For example, if the problem specifies a C-H bond or a C-C bond, note these bonds explicitly.

Consult a table of standard bond-dissociation energies for common bonds in organic molecules. These tables are typically found in textbooks or reliable online resources. For example, the BDE for a C-H bond in methane is approximately 104 kcal/mol, while for a C-C bond in ethane, it is about 88 kcal/mol.

For part (b), if additional inferences are required, analyze the molecular environment of the bond. For instance, if the bond is in a strained ring system or adjacent to an electronegative atom, the BDE may differ from the standard value. Consider how factors like resonance, hybridization, or steric effects might influence the bond strength.

Use the information gathered to approximate the BDE for each bond. If the bond is not directly listed in the table, interpolate or extrapolate based on similar bonds. For example, if the bond is a C-H bond in an sp2 hybridized carbon (as in an alkene), its BDE will be slightly higher than that of a C-H bond in an sp3 hybridized carbon.

Summarize the approximate BDE values for each bond, ensuring that your reasoning and any assumptions made are clearly stated. This will help validate your approximations and provide a logical basis for your conclusions.

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Key Concepts

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

Bond-Dissociation Energy (BDE)

Bond-dissociation energy is the energy required to break a specific bond in a molecule, resulting in the formation of two radicals. It is a measure of bond strength; stronger bonds have higher BDE values. BDE can vary depending on the molecular environment and the types of atoms involved, making it essential for predicting reaction outcomes and stability.

Types of Bonds

In organic chemistry, bonds can be classified as single, double, or triple bonds, each with distinct characteristics and bond-dissociation energies. Single bonds (sigma bonds) are generally weaker than double (one sigma and one pi bond) and triple bonds (one sigma and two pi bonds). Understanding these types helps in estimating BDE and predicting reactivity in chemical reactions.

Resonance and Hybridization

Resonance refers to the delocalization of electrons in a molecule, which can affect bond strength and stability. Hybridization describes the mixing of atomic orbitals to form new hybrid orbitals, influencing bond angles and lengths. Both concepts are crucial for making inferences about bond-dissociation energies, as they can alter the expected values based on molecular structure.

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Related Practice

Textbook Question

Use bond-dissociation enthalpies (Table 4-2, p. 167) to calculate values of ΔH° for the following reactions.

b. CH₃CH₂Cl + HI → CH₃CH₂I + HCl

Textbook Question

Use bond-dissociation enthalpies (Table 4-2, p. 167) to calculate values of ΔH° for the following reactions.

c. (CH₃)₃C—OH + HCl → (CH₃)₃C—Cl + H₂O

Textbook Question

Use bond-dissociation enthalpies (Table 4-2, p. 167) to calculate values of ΔH° for the following reactions.

d. CH₃CH₂CH₃ + H₂ → CH₃CH₃ + CH₄

Textbook Question

If the following reaction is favorable, what can we say about the sign of ∆H°? Explain your answer.

Textbook Question

Calculate ∆H° for the following alkene addition reaction, one we discuss further in Chapter 7. Predict the sign of ∆S° . (The BDE for C―C π bond is approximately 65 kcal/mol.)

Textbook Question

Reaction (c), on the other hand, is favored (∆G° < 0). Identify the bonds formed and broken and explain this result in light of (a) and (b).

(c)

Textbook Question

Calculate ∆H° for the following equilibrium processes.

(b)

Textbook Question

The combustion of alkanes is exothermic (∆H° < 0) . Would you expect the combustion of butane or cyclobutane to be more exothermic?

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