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

2. Molecular Representations

Intermolecular Forces

Organic Chemistry

2. Molecular Representations

Intermolecular Forces

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2:49 minutes

Problem 16a

Textbook Question

Imidazole boils at 257 °C, whereas N-methylimidazole boils at 199 °C. Explain the difference in boiling points.

Verified step by step guidance

Step 1: Begin by analyzing the molecular structures of imidazole and N-methylimidazole. Imidazole is a five-membered aromatic heterocyclic compound containing two nitrogen atoms, one of which is part of an NH group. N-methylimidazole is similar, but the NH group is replaced by an N-CH₃ group.

Step 2: Consider the role of hydrogen bonding in boiling points. Imidazole has an NH group capable of forming strong hydrogen bonds with other molecules, which increases intermolecular forces and raises the boiling point. N-methylimidazole lacks this NH group, so it cannot form hydrogen bonds as effectively.

Step 3: Evaluate the impact of the methyl group in N-methylimidazole. The methyl group is nonpolar and contributes to weaker van der Waals forces compared to the hydrogen bonding in imidazole. This results in a lower boiling point for N-methylimidazole.

Step 4: Discuss the overall intermolecular forces. Imidazole experiences both hydrogen bonding and van der Waals forces, while N-methylimidazole primarily relies on van der Waals forces. Stronger intermolecular forces in imidazole require more energy to overcome, leading to a higher boiling point.

Step 5: Conclude that the difference in boiling points is primarily due to the presence of hydrogen bonding in imidazole, which is absent in N-methylimidazole due to the substitution of the NH group with a methyl group.

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Key Concepts

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

Intermolecular Forces

Intermolecular forces are the attractive forces between molecules that influence physical properties like boiling points. Stronger intermolecular forces, such as hydrogen bonding or dipole-dipole interactions, typically result in higher boiling points. In the case of imidazole and N-methylimidazole, the presence of additional methyl groups in N-methylimidazole alters the hydrogen bonding capabilities, affecting the overall strength of these forces.

Molecular Structure and Polarity

The molecular structure and polarity of a compound significantly impact its boiling point. Imidazole has a planar structure with polar N-H bonds, allowing for effective hydrogen bonding. N-methylimidazole, however, has a methyl group that increases steric hindrance and reduces the molecule's ability to form strong hydrogen bonds, leading to a lower boiling point compared to imidazole.

Boiling Point and Molecular Weight

Boiling point is also influenced by molecular weight, as heavier molecules generally have higher boiling points due to increased van der Waals forces. However, in this case, the difference in boiling points between imidazole and N-methylimidazole is more significantly attributed to the changes in intermolecular forces and molecular structure rather than molecular weight alone, as both compounds have similar molecular weights.

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