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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Problem 38d

Textbook Question

Using bond-dissociation energies, identify the most stable radical. Justify the difference in stability based on the structure.
(d) I• vs •OH

Verified step by step guidance

Identify the bond-dissociation energy (BDE) values for the bonds that would form the radicals I• and •OH. Bond-dissociation energy is the energy required to break a bond homolytically, resulting in two radicals. Look up the BDE for H-I and H-OH bonds in a reliable data source.

Compare the BDE values. A lower BDE indicates that the bond is easier to break, which often correlates with the stability of the resulting radical. This is because a more stable radical requires less energy to form.

Analyze the electronic structure of the radicals. I• is a halogen radical, and its stability is influenced by the large size of the iodine atom, which allows the unpaired electron to be delocalized over a larger volume, reducing electron-electron repulsion. In contrast, •OH is a smaller radical with a highly electronegative oxygen atom, which holds the unpaired electron tightly, making it less stable.

Consider the periodic trends. Iodine is in the same group as other halogens but is much larger and less electronegative than oxygen. This makes I• more stable because the unpaired electron experiences less repulsion and is less tightly held compared to •OH.

Conclude that I• is the more stable radical based on its lower bond-dissociation energy and the ability of iodine to better stabilize the unpaired electron due to its size and lower electronegativity compared to oxygen.

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Key Concepts

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

Bond-Dissociation Energy

Bond-dissociation energy (BDE) is the energy required to break a bond in a molecule, resulting in the formation of radicals. Higher BDE values indicate stronger bonds, which correlate with lower radical stability. Understanding BDE is crucial for comparing the stability of different radicals, as it helps predict which radical is more likely to form based on the energy required to dissociate the bond.

Radical Stability

Radical stability refers to the relative stability of radical species, which are molecules with unpaired electrons. Factors influencing radical stability include the degree of substitution (primary, secondary, tertiary), resonance effects, and electronegativity of adjacent atoms. More substituted radicals or those that can delocalize their unpaired electron through resonance are generally more stable.

Structure-Activity Relationship

Structure-activity relationship (SAR) is a principle that relates the chemical structure of a compound to its biological activity or stability. In the context of radicals, the arrangement of atoms and the presence of functional groups can significantly affect radical stability. Analyzing the structural differences between radicals like I• and •OH helps explain their varying stabilities based on steric and electronic factors.

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Related Practice

Textbook Question

Calculate ∆H° for the following reactions.

Textbook Question

Calculate ∆H° for the following reactions.

(a)

Textbook Question

Using bond-dissociation energies, identify the most stable radical. Justify the difference in stability based on the structure.

(a)

Textbook Question

Using bond-dissociation energies, identify the most stable radical. Justify the difference in stability based on the structure.

(c)

Textbook Question

In the following reactions, identify the bonds formed and the bonds broken.

(a)

Textbook Question

In the following reactions, identify the bonds formed and the bonds broken.

(c)

Textbook Question

Teflon-coated frying pans routinely endure temperatures that would cause polyethylene or polypropylene to oxidize and decompose. Decomposition of polyethylene is initiated by free-radical abstraction of a hydrogen atom by O₂. Bond-dissociation energies of C—H bonds are about 400 kJ/mol, and C—F bonds are about 460 kJ/mol. The BDE of the H—OO bond is about 192 kJ/mol, and the F—OO bond is about 63 kJ/mol. Show why Teflon (Figure 7-5) is much more resistant to oxidation than polyethylene is.

Textbook Question

Use the bond-dissociation enthalpies in Table 4-2 (page 167) to calculate the heats of reaction for the two possible first propagation steps in the chlorination of isobutane. Use this information to draw a reaction-energy diagram like Figure 4-8, comparing the activation energies for formation of the two radicals.

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Using bond-dissociation energies, identify the most stable radical. Justify the difference in stability based on the structure.(d) I• vs •OH

Key Concepts

Bond-Dissociation Energy

Radical Stability

Structure-Activity Relationship

Watch next

Using bond-dissociation energies, identify the most stable radical. Justify the difference in stability based on the structure.
(d) I• vs •OH