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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5:15 minutes

Problem 28

Textbook Question

Why is the pK_a value of protonated hydroxylamine (6.0) so much lower than the value of a protonated primary amine such as protonated methylamine (10.7)?

Verified step by step guidance

Understand the concept of pKa: The pKa value indicates the strength of an acid. A lower pKa value corresponds to a stronger acid, meaning the compound is more likely to donate a proton.

Examine the structure of protonated hydroxylamine: Protonated hydroxylamine has an -OH group attached to the nitrogen atom. The electronegativity of oxygen increases the electron-withdrawing effect, stabilizing the conjugate base after deprotonation and making the protonated form more acidic (lower pKa).

Compare with protonated methylamine: Protonated methylamine has a methyl group (-CH3) attached to the nitrogen atom. The methyl group is electron-donating, which destabilizes the conjugate base after deprotonation, making the protonated form less acidic (higher pKa).

Consider resonance and inductive effects: In protonated hydroxylamine, the lone pairs on the oxygen atom can interact with the nitrogen atom, further stabilizing the conjugate base. This effect is absent in protonated methylamine, contributing to the difference in pKa values.

Summarize the reasoning: The lower pKa value of protonated hydroxylamine compared to protonated methylamine is due to the electron-withdrawing effect of the -OH group and the stabilization of the conjugate base through resonance and inductive effects, making protonated hydroxylamine a stronger acid.

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Key Concepts

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

Protonation and pKa Values

Protonation refers to the addition of a proton (H+) to a molecule, which can significantly affect its acidity and basicity. The pKa value is a quantitative measure of the strength of an acid in solution; lower pKa values indicate stronger acids. In this context, the pKa values of protonated hydroxylamine and protonated methylamine reflect their relative stabilities and tendencies to donate protons.

Resonance Stabilization

Resonance stabilization occurs when a molecule can be represented by multiple valid Lewis structures, allowing for the delocalization of electrons. In the case of protonated hydroxylamine, the positive charge can be delocalized over the nitrogen and oxygen atoms, which can lead to a less stable structure compared to protonated methylamine, where the positive charge is localized on the nitrogen atom.

Inductive Effects

Inductive effects refer to the electron-withdrawing or electron-donating effects of substituents on a molecule, which can influence its acidity or basicity. In protonated methylamine, the alkyl group can donate electron density to the nitrogen, stabilizing the positive charge. In contrast, the presence of the electronegative oxygen in protonated hydroxylamine can withdraw electron density, making it less stable and resulting in a lower pKa.

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Related Practice

Textbook Question

Identify the most stable conjugate base in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer.

(f)

Textbook Question

Identify the most acidic proton in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer. [Always start by drawing the conjugate base.]

(b)

Textbook Question

Identify the most acidic proton in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer. [Always start by drawing the conjugate base.]

(d)

Textbook Question

Which acid in each pair would you expect to more readily donate a proton to a basic compound?

(a)

Textbook Question

In light of your answers to Assessments 24.54 and 24.55, rank the following based on the rate of protonation of the alkene (1 = most basic, 6 = least basic). [Ignore the fact that the alkene may not be the most basic site in the molecule.]

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Consider the following drugs used to treat the indicated diseases. Would you expect the activity of these drugs to be impacted by a patient taking other medicines for acid reflux disease?

Textbook Question

Which is the most stable base in each pair?

Textbook Question

Explain why a base can remove a proton from the α-carbon of N,N-dimethylethanamide but not from the α-carbon of either N-methylethanamide or ethanamide.

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Why is the pKa value of protonated hydroxylamine (6.0) so much lower than the value of a protonated primary amine such as protonated methylamine (10.7)?

Key Concepts

Protonation and pKa Values

Resonance Stabilization

Inductive Effects

Watch next

Why is the pK_a value of protonated hydroxylamine (6.0) so much lower than the value of a protonated primary amine such as protonated methylamine (10.7)?