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

26. Amines

Amine Alkylation

Organic Chemistry

26. Amines

Amine Alkylation

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3:11 minutes

Problem 61a

Textbook Question

Basicity depends on availability of an electron pair to bond a proton. Correlate structural effects in these amines with their basicities.
(a) Explain this order:

Verified step by step guidance

Step 1: Understand the concept of basicity. Basicity in amines depends on the availability of the lone pair of electrons on the nitrogen atom to bond with a proton (H⁺). Structural factors such as resonance, inductive effects, and steric hindrance can influence the availability of this lone pair.

Step 2: Analyze the structure of the first compound (N(CH₃)₂ attached to a benzene ring, pKb = 8.9). The nitrogen atom is part of a dimethylamino group, which is electron-donating due to the alkyl groups. This increases the availability of the lone pair on nitrogen, making it more basic. Additionally, the lone pair is not involved in resonance with the benzene ring, further enhancing basicity.

Step 3: Examine the structure of the second compound (a bicyclic amine, pKb = 6.2). The nitrogen atom is part of a bicyclic system where its lone pair is partially delocalized due to resonance with the adjacent aromatic ring. This delocalization reduces the availability of the lone pair for bonding with a proton, decreasing basicity compared to the first compound.

Step 4: Evaluate the structure of the third compound (a pyridine-like structure, pKb = 3.4). The nitrogen atom is part of an aromatic ring, and its lone pair is fully delocalized into the aromatic system. This extensive resonance significantly reduces the availability of the lone pair for bonding with a proton, making it the least basic among the three compounds.

Step 5: Correlate the pKb values with basicity. A higher pKb value corresponds to lower basicity, while a lower pKb value indicates higher basicity. The order of basicity is: N(CH₃)₂ attached to benzene (most basic, pKb = 8.9) > bicyclic amine (moderately basic, pKb = 6.2) > pyridine-like structure (least basic, pKb = 3.4). This order is explained by the structural effects on the availability of the nitrogen's lone pair.

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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 amines refers to their ability to accept protons (H+) due to the presence of a lone pair of electrons on the nitrogen atom. The strength of an amine's basicity is influenced by the availability of this lone pair, which can be affected by the surrounding structural environment, such as steric hindrance and electronic effects.

Inductive Effect

The inductive effect describes how electron-withdrawing or electron-donating groups attached to a molecule can influence the electron density on the nitrogen atom of an amine. Electron-withdrawing groups decrease basicity by stabilizing the lone pair, while electron-donating groups enhance basicity by increasing electron density, making the lone pair more available for bonding with protons.

Steric Hindrance

Steric hindrance refers to the repulsion that occurs when bulky groups are present near the reactive site of a molecule, in this case, the nitrogen atom of an amine. Increased steric hindrance can hinder the approach of protons, thereby reducing the basicity of the amine. Understanding the spatial arrangement of substituents is crucial for predicting the basicity order among different amines.

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(c)

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Textbook Question

Basicity depends on availability of an electron pair to bond a proton. Correlate structural effects in these amines with their basicities.

(b) Explain:

Textbook Question

Basicity depends on availability of an electron pair to bond a proton. Correlate structural effects in these amines with their basicities.

(c) The pK_b of this compound is −2.3, making it not only a stronger base than a typical aniline, but even stronger than hydroxide ion. Explain its remarkable basicity.

Textbook Question

Rank the amines in each set in order of increasing basicity.

(d)

Textbook Question

Within each structure, rank the indicated nitrogens by increasing basicity.

(f)

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