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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3:58 minutes

Problem 41b,c,d

Textbook Question

The following compounds are listed in increasing order of acidity. In each case, the most acidic proton is shown in red.

b. Explain why X is a stronger acid than W.
c. Explain why Y is a stronger acid than X.
d. Explain why Z is a stronger acid than Y.

Verified step by step guidance

Identify the structural differences between compounds W and X. Compound W has a methylene group (CH2) adjacent to the carbonyl, while compound X has an amide group (NH).

Consider the effect of the amide group in X. The nitrogen in the amide can participate in resonance with the carbonyl group, stabilizing the conjugate base more effectively than the methylene group in W.

Examine the structural difference between compounds X and Y. Compound Y has an additional hydroxyl group (OH) attached to the nitrogen, forming a hydroxamic acid.

Analyze the effect of the hydroxyl group in Y. The presence of the OH group increases the acidity by allowing additional resonance stabilization of the conjugate base, as well as potential hydrogen bonding interactions.

Compare compounds Y and Z. Compound Z is a carboxylic acid, which is generally more acidic due to the high resonance stabilization of its conjugate base (carboxylate ion) and the electronegative oxygen atoms that stabilize the negative charge.

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Key Concepts

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

Acidity and pKa

Acidity in organic chemistry is often measured using the pKa value, which indicates the strength of an acid. A lower pKa value corresponds to a stronger acid, meaning it more readily donates protons (H+). Understanding the relationship between pKa and acidity is crucial for comparing the acidity of different compounds.

Resonance Stabilization

Resonance stabilization occurs when a molecule can distribute its electron density across multiple structures, leading to increased stability. In the context of acidity, if the conjugate base formed after deprotonation can be stabilized by resonance, the original acid will be stronger. This concept helps explain why certain compounds have lower pKa values.

Inductive Effect

The inductive effect refers to the electron-withdrawing or electron-donating effects of substituents on a molecule. Electronegative atoms or groups can stabilize the negative charge on a conjugate base through inductive withdrawal, enhancing acidity. This effect is important in comparing the acidity of compounds with different substituents.

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Related Practice

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).

c. Compare the most stable conjugate base of ascorbic acid with the conjugate base of acetic acid, and suggest why these two compounds have similar acidities, even though ascorbic acid lacks the carboxylic acid (COOH) group.

Textbook Question

Rank the following acids in decreasing order of their acid strength. In each case, explain why the previous compound should be a stronger acid than the one that follows it.

Textbook Question

The following compound can become protonated on any of the three nitrogen atoms. One of these nitrogens is much more basic than the others, however.

b. Determine which nitrogen atom is the most basic.

Textbook Question

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

(a)

(b)

Textbook Question

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

(a)

(b)

(c)

Textbook Question

The following compounds can all react as acids.

c. Rank the original compounds in order, from strongest acid to weakest acid.

Textbook Question

Consider the type of orbitals involved, and rank the following nitrogen compounds in order of decreasing basicity. 2. Rank the conjugate acids in order of increasing acidity. (Hint: These two orders should be the same!)

Textbook Question

Consider each pair of bases, and explain which one is more basic. Draw their conjugate acids, and show which one is a stronger acid.

(a)

(b)

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