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

24. Enolate Chemistry: Reactions at the Alpha-Carbon

Enolate

Organic Chemistry

24. Enolate Chemistry: Reactions at the Alpha-Carbon

Enolate

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3:01 minutes

Problem 60e

Textbook Question

For each molecule shown below,
1. indicate the most acidic hydrogens.
2. draw the important resonance contributors of the anion that results from removal of the most acidic hydrogen.
(e)

Verified step by step guidance

Step 1: Identify the functional groups in the molecule. The molecule contains a ketone group (C=O) and an ester group (COOCH₃). These groups influence the acidity of hydrogens in the molecule due to their electron-withdrawing effects.

Step 2: Determine the most acidic hydrogen. The hydrogens alpha to the ketone group (on the carbon adjacent to the C=O group) are the most acidic. This is because the negative charge formed upon deprotonation can be stabilized by resonance with the ketone group.

Step 3: Remove the most acidic hydrogen to form the anion. Deprotonation of the alpha hydrogen results in a carbanion on the alpha carbon.

Step 4: Draw the resonance contributors of the resulting anion. The negative charge on the alpha carbon can delocalize into the ketone group, forming resonance structures where the negative charge is on the oxygen atom of the ketone group. Additionally, the ester group may also participate in resonance stabilization.

Step 5: Ensure all resonance structures are valid. Verify that each resonance structure follows the rules of resonance, including maintaining the octet rule for all atoms and proper placement of charges.

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Key Concepts

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

Acidity of Hydrogens

In organic chemistry, the acidity of a hydrogen atom is determined by its ability to be removed as a proton (H+). Factors influencing acidity include the electronegativity of the atom to which the hydrogen is attached, the stability of the resulting anion, and the presence of electron-withdrawing groups. In the given molecule, the most acidic hydrogens are typically those adjacent to carbonyl groups or other electronegative atoms.

Resonance Structures

Resonance structures are different ways of drawing a molecule that represent the same compound, showing the delocalization of electrons. In the context of the question, after removing the most acidic hydrogen, the resulting anion can be stabilized by resonance, where the negative charge is distributed over multiple atoms. This delocalization lowers the energy of the anion, making it more stable.

Anion Stability

The stability of an anion is crucial in determining the acidity of the corresponding acid. Anions that can delocalize their negative charge through resonance or are stabilized by inductive effects from nearby electronegative atoms are generally more stable. In the case of the molecule provided, the anion formed after deprotonation will be more stable due to resonance with the carbonyl group, which can help distribute the negative charge.

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Related Practice

Textbook Question

Give the important resonance forms for the possible enolate ions of the following:

(f)

Textbook Question

Show the resonance forms for the enolate ions that result when the following compounds are treated with a strong base.

(a) ethyl acetoacetate

(b) pentane-2,4-dione

Textbook Question

When cis-2,4-dimethylcyclohexanone is dissolved in aqueous ethanol containing a trace of NaOH, a mixture of cis and trans isomers results. Propose a mechanism for this isomerization.

Textbook Question

For each molecule shown below,

1. indicate the most acidic hydrogens.

2. draw the important resonance contributors of the anion that results from removal of the most acidic hydrogen.

(d)

Textbook Question

Phenylacetone can form two different enols.

(a) Show the structures of these enols.

(b) Predict which enol will be present in the larger concentration at equilibrium.

Textbook Question

For each molecule shown below,

1. indicate the most acidic hydrogens.