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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6:30 minutes

Problem 52h

Textbook Question

Identify the most acidic proton in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer. [Always start by drawing the conjugate base.]
(h)

Verified step by step guidance

Start by drawing the conjugate base for each molecule in the pair. To do this, remove one proton (H⁺) from each molecule and represent the resulting structure. This step is crucial because the stability of the conjugate base determines the acidity of the proton.

Analyze the stability of the conjugate base formed. Look for structural features such as resonance stabilization, inductive effects, and hybridization of the atom bearing the negative charge. Resonance stabilization is particularly important because it delocalizes the negative charge, making the conjugate base more stable.

Consider the electronegativity of the atom that bears the negative charge in the conjugate base. A more electronegative atom can better stabilize the negative charge, increasing the acidity of the proton attached to it.

Evaluate the inductive effects caused by nearby electronegative atoms or groups. Electronegative substituents can pull electron density away from the negatively charged atom in the conjugate base, stabilizing it further and increasing the acidity of the proton.

Compare the conjugate bases of the two molecules in the pair based on the above factors (resonance, electronegativity, inductive effects, and hybridization). The proton whose removal leads to the more stable conjugate base is the most acidic proton in the pair.

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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 refers to the tendency 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 identifying the most acidic proton in a given pair, as it allows for comparison of the stability of the conjugate bases formed after deprotonation.

Conjugate Base Stability

The stability of a conjugate base significantly influences the acidity of the corresponding acid. Factors such as electronegativity, resonance, and inductive effects can stabilize the negative charge on the conjugate base. When analyzing pairs of acids, one must consider how these structural features affect the stability of the conjugate bases, as a more stable conjugate base corresponds to a stronger acid.

Resonance and Inductive Effects

Resonance involves the delocalization of electrons across multiple atoms, which can stabilize a conjugate base by spreading out the negative charge. Inductive effects refer to the influence of electronegative atoms or groups that can withdraw electron density, further stabilizing the conjugate base. Both resonance and inductive effects are critical in determining which proton is more acidic, as they directly impact the stability of the resulting conjugate base.

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Related Practice

Textbook Question

Using qualitative reasoning for the acid–base reactions shown,

(i) which is stronger, the base or the conjugate base?

(ii) Which side of the reaction is favored?

(iii) Would you expect a K_eq greater than or less than 1?

(a)

Textbook Question

Identify the most stable conjugate base in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer.

(c)

Textbook Question

Identify the most stable conjugate base in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer.

(e)

Textbook Question

Identify the most acidic proton in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer. [Always start by drawing the conjugate base.]

(a)

Textbook Question

Which anion in each pair would you expect to react more quickly with H⁺?

(a)

Textbook Question

Which anion in each pair would you expect to react more quickly with H⁺?

(b)

Textbook Question

If reacted with a strong base, which of the labeled protons would you expect to be removed first?

Textbook Question

Which is the most acidic compound in each pair?

(a)