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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4:35 minutes

Problem 31

Textbook Question

Acetylacetone (pentane-2,4-dione) reacts with sodium hydroxide to give water and the sodium salt of a carbanion. Write a complete structural formula for the carbanion, and use resonance forms to show the stabilization of the carbanion.

Verified step by step guidance

Identify the acidic hydrogen in acetylacetone. The hydrogen atom on the carbon between the two carbonyl groups (CH2) is acidic due to the electron-withdrawing effect of the carbonyl groups.

When acetylacetone reacts with sodium hydroxide, the hydroxide ion (OH-) abstracts the acidic hydrogen, forming water and leaving behind a carbanion at the central carbon.

Draw the carbanion structure: The central carbon now has a negative charge, represented as CH2^- between the two carbonyl groups.

Illustrate resonance stabilization: The negative charge on the carbanion can be delocalized to the oxygen atoms of the carbonyl groups. Draw resonance structures showing the negative charge moving to each oxygen atom, forming enolate ions.

Explain the resonance: The resonance forms show that the negative charge is shared between the central carbon and the oxygen atoms, which stabilizes the carbanion through resonance delocalization.

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Key Concepts

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

Carbanions

Carbanions are negatively charged species that contain a carbon atom with three bonds and a lone pair of electrons. They are typically formed when a carbon atom gains an electron, resulting in a formal negative charge. Carbanions are important intermediates in organic reactions, often acting as nucleophiles due to their high electron density.

Resonance Stabilization

Resonance stabilization occurs when a molecule can be represented by two or more valid Lewis structures, known as resonance forms. These forms contribute to the overall stability of the molecule, as the actual structure is a hybrid of these forms. In the case of carbanions, resonance can delocalize the negative charge over multiple atoms, reducing the energy and increasing stability.

Acetylacetone Reactivity

Acetylacetone (pentane-2,4-dione) is a β-diketone that can easily form enolates in the presence of a base like sodium hydroxide. The deprotonation of one of the acidic hydrogen atoms adjacent to the carbonyl groups leads to the formation of a carbanion. This reaction is significant in organic synthesis, as it allows for the formation of various derivatives through nucleophilic substitution.

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Related Practice

Textbook Question

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

Textbook Question

The following compounds can all react as bases.

b. Rank the conjugate acids in the order you would predict, from most stable to least stable.

Textbook Question

Four pairs of compounds are shown. In each pair, one of the compounds reacts more quickly, or with a more favorable equilibrium constant, than the less conjugated system. In each case, explain the enhanced reactivity.

(d)

Textbook Question

Use resonance forms of the conjugate bases to explain why methanesulfonic acid (CH₃SO₃H, pK_a = –2.6) is a much stronger acid than acetic acid (CH₃COOH, pK_a = 4.8).

Textbook Question

Identify the stronger base in each pair. Explain your choice. Citing pK_a values is not an acceptable answer.

(a)

Textbook Question

Identify the stronger base in each pair. Explain your choice. Citing pK_a values is not an acceptable answer.

(c)

Textbook Question

Identify the stronger acid in each pair. Explain your choice. Citing pK_a values is not an acceptable answer.

(a)

Textbook Question

Without using pK_a values, pick out the least reactive (most stable) base in each pair. Explain your answer.

(a)

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