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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5:09 minutes

Problem 85

Textbook Question

Rank the indicated hydrogen in the following compounds from most acidic to least acidic:

Verified step by step guidance

Step 1: Identify the functional groups in each compound. In compound (a), the hydrogens are alpha to two ketone groups. In compound (b), the hydrogens are alpha to two ketone groups but separated by an additional carbon. In compound (c), the hydrogens are alpha to one ketone group.

Step 2: Recall that the acidity of alpha hydrogens is influenced by the electron-withdrawing effects of nearby carbonyl groups. The more carbonyl groups present and the closer they are to the alpha hydrogens, the more acidic the hydrogens will be.

Step 3: Analyze compound (a). The alpha hydrogens are flanked by two ketone groups directly, which strongly stabilize the conjugate base through resonance, making these hydrogens highly acidic.

Step 4: Analyze compound (b). The alpha hydrogens are also flanked by two ketone groups, but the ketones are separated by an additional carbon. This reduces the resonance stabilization compared to compound (a), making these hydrogens less acidic than those in (a).

Step 5: Analyze compound (c). The alpha hydrogens are flanked by only one ketone group, providing less resonance stabilization compared to compounds (a) and (b). Therefore, these hydrogens are the least acidic.

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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 structure and acidity is crucial, as factors like electronegativity and resonance can significantly influence a compound's ability to release a proton.

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 negative charge that forms when an acid donates a proton, making the compound more acidic. Identifying resonance structures helps predict which hydrogen atoms are more acidic based on their ability to stabilize the resulting anion.

Inductive Effect

The inductive effect refers to the electron-withdrawing or electron-donating effects of substituents on a molecule, which can influence acidity. Electronegative atoms or groups can pull electron density away from the hydrogen atom, stabilizing the conjugate base and increasing acidity. Understanding how different substituents affect the acidity of hydrogen atoms is essential for ranking their acidity in organic compounds.

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