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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7:03 minutes

Problem 22a,b

Textbook Question

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

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Identify the functional groups in each compound. Both compounds in pair (b) are enolates, which are conjugate bases of enols.

Consider the resonance stabilization of the enolate ion. The more resonance structures available, the more stable the enolate ion, and thus the less basic it is.

Examine the position of the double bond in each enolate. In the first compound, the double bond is conjugated with the carbonyl group, allowing for resonance stabilization.

In the second compound, the double bond is not conjugated with the carbonyl group, which limits resonance stabilization.

Conclude that the enolate with the conjugated double bond (first compound) is more stable and therefore less basic. Thus, the second compound is more basic due to less resonance stabilization.

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Key Concepts

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

Basicity of Amines

Basicity in organic chemistry refers to the ability of a compound to accept protons (H+ ions). Amines, which contain a nitrogen atom with a lone pair of electrons, are generally basic because they can donate this lone pair to bond with protons. The strength of an amine's basicity can be influenced by the surrounding molecular structure and the presence of electron-withdrawing or electron-donating groups.

Resonance Effects

Resonance refers to the delocalization of electrons in a molecule, which can stabilize certain structures. In the context of basicity, if an amine is part of a resonance-stabilized system, the lone pair on the nitrogen may be involved in resonance, making it less available to bond with protons. This can decrease the basicity of the amine compared to one where the lone pair is more localized and available.

Steric Hindrance

Steric hindrance occurs when bulky groups around a reactive site impede the approach of other molecules or ions. In the case of amines, if the nitrogen atom is surrounded by large substituents, it may be less accessible for protonation, thus reducing its basicity. Understanding the spatial arrangement of atoms in isomers is crucial for predicting their reactivity and basicity.

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Related Practice

Textbook Question

Which is a stronger acid?

c. CH₃OCH₂CH₂CH₂OHorCH₃CH₂OCH₂CH₂OH

Textbook Question

The pK_a of ascorbic acid (vitamin C, page 55) is 4.17, showing that it is slightly more acidic than acetic acid (CH₃COOH, pK_a 4.74).

c. Compare the most stable conjugate base of ascorbic acid with the conjugate base of acetic acid, and suggest why these two compounds have similar acidities, even though ascorbic acid lacks the carboxylic acid (COOH) group.

Textbook Question

Rank the following acids in decreasing order of their acid strength. In each case, explain why the previous compound should be a stronger acid than the one that follows it.

Textbook Question

The following compound can become protonated on any of the three nitrogen atoms. One of these nitrogens is much more basic than the others, however.

b. Determine which nitrogen atom is the most basic.

Textbook Question

The following compounds are listed in increasing order of acidity. In each case, the most acidic proton is shown in red.

b. Explain why X is a stronger acid than W.

c. Explain why Y is a stronger acid than X.

d. Explain why Z is a stronger acid than Y.

Textbook Question

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

(a)

(b)

(c)

Textbook Question

The following compounds can all react as acids.

c. Rank the original compounds in order, from strongest acid to weakest acid.

Textbook Question

Consider the type of orbitals involved, and rank the following nitrogen compounds in order of decreasing basicity. 2. Rank the conjugate acids in order of increasing acidity. (Hint: These two orders should be the same!)

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

Key Concepts

Basicity of Amines

Resonance Effects

Steric Hindrance

Watch next

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