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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Problem 39b

Textbook Question

In each pair, choose the most acidic compound. Justify your answer. The most acidic proton in each compound has been indicated.
(b)

Verified step by step guidance

Step 1: Identify the acidic proton in each compound. In both compounds, the acidic proton is attached to the nitrogen atom in the amide functional group, as indicated by the blue arrows.

Step 2: Analyze the electronic effects of substituents near the acidic proton. In the first compound, there is a bromine atom attached to the carbon adjacent to the carbonyl group. Bromine is an electronegative atom and can exert an inductive effect, pulling electron density away from the nitrogen and carbonyl group, thereby stabilizing the conjugate base formed after deprotonation.

Step 3: Compare the second compound. The second compound lacks the bromine substituent, meaning it does not benefit from the additional stabilization provided by the inductive effect of bromine. This makes the conjugate base of the second compound less stable compared to the first compound.

Step 4: Recall that the stability of the conjugate base is directly related to the acidity of the compound. A more stable conjugate base corresponds to a more acidic compound.

Step 5: Conclude that the first compound, with the bromine substituent, is more acidic than the second compound due to the inductive electron-withdrawing effect of bromine, which stabilizes the conjugate base.

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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 refers to the ability of a compound to donate a proton (H+). The strength of an acid is often measured by its pKa value; lower pKa values indicate stronger acids. Understanding the relationship between acidity and pKa is crucial for comparing the acidity of different compounds.

Resonance Stabilization

Resonance stabilization occurs when a compound can distribute its electron density across multiple structures, leading to increased stability. In the context of acidity, if the conjugate base formed after deprotonation is resonance-stabilized, the original compound is likely to be more acidic due to the lower energy of the conjugate base.

Inductive Effect

The inductive effect refers to the electron-withdrawing or electron-donating effects of substituents attached to a molecule. Electronegative atoms or groups can stabilize a negative charge on the conjugate base through the inductive effect, thereby increasing the acidity of the original compound. Understanding this concept helps in predicting acidity trends among different compounds.

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Related Practice

Textbook Question

For each of the following substituents, indicate whether it withdraws electrons inductively, donates electrons by hyperconjugation, withdraws electrons by resonance, or donates electrons by resonance.

a. Br

b. CH₂CH₃

Textbook Question

Which loses a proton more readily: a methyl group bonded to cyclohexane or a methyl group bonded to benzene?

Textbook Question

A nitro group (–NO₂) effectively stabilizes a negative charge on an adjacent carbon atom through resonance:

Two of the following nitrophenols are much more acidic than phenol itself. The third compound is only slightly more acidic than phenol. Use resonance structures of the appropriate phenoxide ions to show why two of these anions should be unusually stable.

Textbook Question

In each pair, choose the most basic compound. Justify your answer.

(d)

Textbook Question

Which of the following indicated atoms would you expect to be most basic?

(c)

Textbook Question

Rationalize the difference in pKₐ values for the two hydroxyl groups.

Textbook Question

Rank the compounds in each of the following groups from strongest acid to weakest acid:

Textbook Question

Explain why the $α$ -hydrogen of an N,N-disubstituted amide is less acidic (pK_a = 30) than the $α$ -hydrogen of an ester (pK_a = 25).