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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5:40 minutes

Problem 21

Textbook Question

Rank the carbanions shown in the margin from most basic to least basic.
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Verified step by step guidance

Identify the carbanions in the problem and note the groups or atoms attached to the negatively charged carbon atom. The basicity of a carbanion is influenced by the stability of the negative charge on the carbon atom.

Recall that the stability of a carbanion is inversely related to its basicity. A more stable carbanion is less basic, while a less stable carbanion is more basic.

Analyze the electronic effects of substituents attached to the carbanion. For example, electron-withdrawing groups (e.g., -NO₂, -Cl) stabilize the negative charge through inductive or resonance effects, reducing basicity. Conversely, electron-donating groups (e.g., -CH₃, -OCH₃) destabilize the negative charge, increasing basicity.

Consider the hybridization of the carbon atom bearing the negative charge. Carbanions with sp-hybridized carbons (e.g., alkynyl carbanions) are more stable and less basic than those with sp² or sp³ hybridized carbons due to increased s-character.

Rank the carbanions from most basic to least basic based on the above factors, starting with the carbanion that has the least stabilization of its negative charge (most basic) and ending with the carbanion that has the most stabilization of its negative charge (least basic).

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Key Concepts

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

Carbanion Stability

Carbanion stability is a crucial factor in determining the basicity of a carbanion. A more stable carbanion is less basic because it is less likely to donate its lone pair of electrons. Factors influencing stability include the electronegativity of adjacent atoms, resonance stabilization, and hybridization of the carbon atom bearing the negative charge.

Basicity and pKa

Basicity refers to the ability of a species to accept protons (H+). In organic chemistry, the strength of a base is often correlated with the pKa of its conjugate acid; a lower pKa indicates a stronger acid and thus a weaker base. Understanding the relationship between basicity and pKa is essential for ranking carbanions based on their basicity.

Inductive Effect

The inductive effect describes how the presence of electronegative atoms or groups can stabilize or destabilize a carbanion through the transmission of charge. Electron-withdrawing groups can stabilize a negative charge, making the carbanion less basic, while electron-donating groups can destabilize it, increasing basicity. Recognizing these effects is vital for ranking carbanions.

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Related Practice

Textbook Question

Which is a stronger acid?

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d. CH₃CH₂CH₂OH or CH₃CH₂CH₂SH

Textbook Question

Which is a stronger acid?

Textbook Question

For each of the following compounds, indicate the atom that is protonated when an acid is added to a solution of the compound.

Textbook Question

For each of the following compounds, indicate the atom that is protonated when an acid is added to a solution of the compound.

Textbook Question

b. How does the presence of an electronegative substituent such as Cl affect the acidity of a carboxylic acid?

c. How does the location of the substituent affect the acidity of the carboxylic acid?

Textbook Question

Explain the relative acidities.

CH₂═CHCH₂OH, CH₃CH₂CH₂OH, HC≡CCH₂OH

Textbook Question

Using the table of pK_a values given in [Appendix I] , answer the following:

d. Which is more electronegative: an sp³ oxygen or an sp² oxygen?

e. Which compounds demonstrate that the relative electronegativities of a hybridized nitrogen atom are sp > sp² > sp³?

Textbook Question

Imidazole has two potentially basic sites (a and b). Of the two, where would you expect a proton to add preferentially?

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Rank the carbanions shown in the margin from most basic to least basic.<IMAGE>

Key Concepts

Carbanion Stability

Basicity and pKa

Inductive Effect

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Rank the carbanions shown in the margin from most basic to least basic.
<IMAGE>