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

3. Acids and Bases

Ranking Acidity

Organic Chemistry

3. Acids and Bases

Ranking Acidity

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4:02 minutes

Problem 46b

Textbook Question

The following compounds can all react as bases.

b. Rank the conjugate acids in the order you would predict, from most stable to least stable.

Verified step by step guidance

Identify the conjugate acids of each base. For each base, add a proton (H⁺) to the atom that can accept it. For example, for CH₃CH₂NH₂, the conjugate acid is CH₃CH₂NH₃⁺.

Consider the stability of each conjugate acid. Stability is often influenced by factors such as resonance, inductive effects, and the electronegativity of the atom bearing the positive charge.

Evaluate the resonance stabilization. For example, the conjugate acid of CH₃CONH₂ can be resonance stabilized due to the adjacent carbonyl group.

Assess the inductive effects. Electronegative atoms or groups can stabilize a positive charge through the inductive effect. For instance, the presence of an electronegative oxygen in CH₃CH₂OH can stabilize the conjugate acid.

Rank the conjugate acids from most stable to least stable based on the above evaluations. Consider the overall effect of resonance, inductive effects, and electronegativity on the stability of each conjugate acid.

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Key Concepts

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

Conjugate Acid-Base Pairs

In acid-base chemistry, a conjugate acid-base pair consists of two species that transform into each other by the gain or loss of a proton (H+). When a base gains a proton, it forms its conjugate acid. Understanding the stability of conjugate acids is crucial for predicting the strength of the original bases, as more stable conjugate acids correspond to weaker bases.

Acid Stability and Resonance

The stability of a conjugate acid is often influenced by resonance, which delocalizes charge over multiple atoms, reducing the energy of the molecule. For example, amides can stabilize their conjugate acids through resonance between the nitrogen and the carbonyl group, making them more stable compared to non-resonance-stabilized species. This concept helps in ranking the stability of conjugate acids.

Electronegativity and Inductive Effects

Electronegativity and inductive effects play a significant role in acid stability. Electronegative atoms or groups can stabilize a conjugate acid by withdrawing electron density through sigma bonds, known as the inductive effect. This effect can enhance the stability of a conjugate acid by dispersing charge, making it a key factor in determining the relative stability of different conjugate acids.

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Related Practice

Textbook Question

Choose the more acidic member of each pair of isomers, and show why the acid you chose is more acidic.

(f)

(g)

Textbook Question

The pK_a of ascorbic acid (vitamin C, page 55) is 4.17, showing that it is slightly more acidic than acetic acid (CH₃COOH, pK_a 4.74).

a. Show the four different conjugate bases that would be formed by deprotonation of the four different OH groups in ascorbic acid.

b. Compare the stabilities of these four conjugate bases, and predict which OH group of ascorbic acid is the most acidic.

Textbook Question

Choose the more basic member of each pair of isomers, and show why the base you chose is more basic.

Textbook Question

Choose the more basic member of each pair of isomers, and show why the base you chose is more basic.

Textbook Question

Four pairs of compounds are shown. In each pair, one of the compounds reacts more quickly, or with a more favorable equilibrium constant, than the less conjugated system. In each case, explain the enhanced reactivity.

(d)

Textbook Question

Use resonance forms of the conjugate bases to explain why methanesulfonic acid (CH₃SO₃H, pK_a = –2.6) is a much stronger acid than acetic acid (CH₃COOH, pK_a = 4.8).

Textbook Question

Acetylacetone (pentane-2,4-dione) reacts with sodium hydroxide to give water and the sodium salt of a carbanion. Write a complete structural formula for the carbanion, and use resonance forms to show the stabilization of the carbanion.

Textbook Question

Identify the stronger base in each pair. Explain your choice. Citing pK_a values is not an acceptable answer.

(a)

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