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

Acids and Bases

Organic Chemistry

3. Acids and Bases

Acids and Bases

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3:10 minutes

Problem 18a

Textbook Question

Specify which in each pair is the harder Lewis acid. Justify your choice beyond just looking at Table 20.2.
(a) Al³⁺ vs. B³⁺

Verified step by step guidance

Step 1: Recall the definition of a Lewis acid. A Lewis acid is a species that can accept a pair of electrons. The strength of a Lewis acid depends on factors such as charge density, electronegativity, and the size of the ion.

Step 2: Compare the charges of Al³⁺ and B³⁺. Both ions have a +3 charge, which means they have the same formal charge. However, the size of the ion and its charge density will play a significant role in determining which is the harder Lewis acid.

Step 3: Consider the size of the ions. Aluminum (Al) is in Period 3 of the periodic table, while boron (B) is in Period 2. This means that Al³⁺ is larger in size compared to B³⁺. A smaller ion like B³⁺ will have a higher charge density because the +3 charge is concentrated over a smaller volume.

Step 4: Analyze the charge density. Since B³⁺ has a smaller ionic radius and a higher charge density compared to Al³⁺, it will have a stronger ability to attract electron pairs, making it a harder Lewis acid.

Step 5: Conclude that B³⁺ is the harder Lewis acid due to its smaller size and higher charge density, which increases its ability to accept electron pairs. This conclusion is based on fundamental principles of charge density and periodic trends, not just referencing a table.

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Key Concepts

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

Lewis Acids and Bases

Lewis acids are defined as electron pair acceptors, while Lewis bases are electron pair donors. This concept is fundamental in understanding acid-base reactions in organic chemistry, as it expands the traditional Brønsted-Lowry definitions. The strength of a Lewis acid is influenced by its ability to stabilize the resulting complex after accepting an electron pair.

Charge Density

Charge density refers to the distribution of electric charge over a given volume. In the context of Lewis acids, a higher charge density typically indicates a stronger acid, as it can attract electron pairs more effectively. For cations like Al³⁺ and B³⁺, the charge density is influenced by their ionic radii and the magnitude of their positive charge.

Stability of the Conjugate Base

The stability of the conjugate base formed after a Lewis acid accepts an electron pair is crucial in determining the strength of the acid. A more stable conjugate base will favor the forward reaction, making the original species a stronger Lewis acid. Factors such as electronegativity and resonance can significantly affect the stability of the conjugate base.

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Textbook Question

In addition to radicals, anions, and cations, a fourth class of reactive intermediates is carbenes. A neutral species, the simplest carbene has a molecular formula of CH₂.

Textbook Question

Suggest an arrow-pushing mechanism for the following reaction. Is the hydroxyl group acting as a base, acid, Lewis base, or Lewis acid?

Textbook Question

What is the major product of the following reactions?

Textbook Question

Specify which in each pair is the harder Lewis base. Justify your choice beyond just looking at Table 20.2.

(b)

Textbook Question

Suggest an arrow-pushing mechanism for each of the following acid–base reactions.

(d) [an intramolecular reaction]

Textbook Question

Draw two important resonance structures involving the C―O π bond for the molecule shown. To which carbons would you expect a nucleophile to add?

Textbook Question

Suggest an arrow-pushing mechanism that accounts for the formation of the following Lewis acid–Lewis base complexes. Label the Lewis acid and Lewis base in each.

(a)

Textbook Question

For each of the following reactions, identify the bonds that are broken and formed. Be sure to indicate whether the bond that is broken is a σ bond or a π bond.

(a)

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Specify which in each pair is the harder Lewis acid. Justify your choice beyond just looking at Table 20.2. (a) Al3+ vs. B3+

Key Concepts

Lewis Acids and Bases

Charge Density

Stability of the Conjugate Base

Watch next

Specify which in each pair is the harder Lewis acid. Justify your choice beyond just looking at Table 20.2.
(a) Al³⁺ vs. B³⁺