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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6:27 minutes

Problem 21c,d

Textbook Question

Which acid in each of the following pairs is stronger?
c.
d.

Verified step by step guidance

Step 1: Analyze the molecular structures in pair (c). The first molecule (i) is cyclohexanecarboxylic acid, while the second molecule (ii) is cyclohexanecarboxylic acid with a ketone group attached to the ring. The ketone group is an electron-withdrawing group.

Step 2: Understand the effect of electron-withdrawing groups on acidity. Electron-withdrawing groups stabilize the conjugate base by delocalizing the negative charge, making the acid stronger.

Step 3: Compare the two molecules in pair (c). The ketone group in molecule (ii) increases the acidity of the carboxylic acid group compared to molecule (i), which lacks the electron-withdrawing ketone group.

Step 4: Analyze the molecular structures in pair (d). The first molecule (i) is cyclopentanecarboxylic acid, while the second molecule (ii) is cyclopentanecarboxylic acid with an amine group (-NH) attached to the ring. The amine group is an electron-donating group.

Step 5: Understand the effect of electron-donating groups on acidity. Electron-donating groups destabilize the conjugate base by increasing electron density, making the acid weaker. Therefore, molecule (i) is stronger than molecule (ii) in pair (d).

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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+) in solution. The strength of an acid is often measured by its pKa value; lower pKa values indicate stronger acids. Understanding the relationship between structure and acidity is crucial, as factors like electronegativity and resonance can significantly influence a compound's ability to stabilize the negative charge of its conjugate base.

Resonance Stabilization

Resonance stabilization occurs when a molecule can be represented by multiple valid Lewis structures, allowing for the delocalization of electrons. This delocalization can stabilize the conjugate base formed after deprotonation, making the original acid stronger. In the context of the question, comparing the resonance effects in the given acid structures will help determine which acid is stronger.

Inductive Effect

The inductive effect refers to the electron-withdrawing or electron-donating effects transmitted through sigma bonds in a molecule. Electronegative atoms or groups can stabilize the negative charge of a conjugate base through the inductive effect, enhancing acidity. Analyzing the presence of such groups in the acid structures presented will aid in assessing their relative strengths.

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Textbook Question

Which member of each pair is the stronger base?

c. phenolate ion or ethoxide ion

d. phenolate ion or acetate ion

Textbook Question

Which member of each pair is the stronger base?

a. ethylamine or aniline

b. ethylamine or ethoxide ion

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Which acid in each of the following pairs is stronger?

Textbook Question

Purine is a heterocyclic compound with four nitrogen atoms.

a. Which nitrogen is most apt to be protonated?

b. Which nitrogen is least apt to be protonated?

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.

d. NHCH₃

e. OCH₃

f. ⁺N(CH₃)₃

Textbook Question

Explain why the pK_a of p-nitrophenol is 7.14, whereas the pK_a of m-nitrophenol is 8.39.

Textbook Question

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?

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