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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3:58 minutes

Problem 35e,f

Textbook Question

Predict which compound in each pair has the higher boiling point. Explain your prediction.
(e)
(f)

Verified step by step guidance

Step 1: Identify the functional groups present in each compound. In pair (e), the first compound is 3-methylpiperidine, which is a secondary amine, and the second compound is 1,3-dimethylpyrrolidine, which is a tertiary amine. In pair (f), the first compound is 2,4-dimethylpyrrolidine, a secondary amine, and the second compound is 4-methylpyrrolidin-2-one, a lactam (cyclic amide).

Step 2: Consider the effect of hydrogen bonding on boiling points. Secondary amines can form hydrogen bonds due to the presence of an N-H bond, whereas tertiary amines cannot form hydrogen bonds as effectively because they lack an N-H bond. Amides, like the lactam in pair (f), can form strong hydrogen bonds due to the presence of both N-H and C=O groups.

Step 3: Analyze the molecular size and shape. Larger and more complex molecules generally have higher boiling points due to increased van der Waals forces. In pair (e), 3-methylpiperidine has a larger ring size compared to 1,3-dimethylpyrrolidine, which may contribute to a higher boiling point.

Step 4: Evaluate the presence of polar groups. The presence of polar groups like the carbonyl group in 4-methylpyrrolidin-2-one (pair f) can increase boiling points due to dipole-dipole interactions.

Step 5: Predict the boiling points based on the above factors. For pair (e), 3-methylpiperidine is likely to have a higher boiling point due to its ability to form hydrogen bonds and larger size. For pair (f), 4-methylpyrrolidin-2-one is expected to have a higher boiling point due to strong hydrogen bonding and dipole-dipole interactions from the carbonyl group.

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Key Concepts

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

Boiling Point and Intermolecular Forces

The boiling point of a compound is influenced by the strength of its intermolecular forces. Compounds with stronger forces, such as hydrogen bonding or dipole-dipole interactions, typically have higher boiling points. In organic compounds, the presence of functional groups that can engage in hydrogen bonding significantly raises the boiling point compared to those that cannot.

Hydrogen Bonding

Hydrogen bonding occurs when a hydrogen atom covalently bonded to a highly electronegative atom, like nitrogen, interacts with another electronegative atom. In the context of the compounds presented, the cyclic amine with an NH group can form hydrogen bonds, which enhances its boiling point compared to the compound with a methyl group attached to nitrogen, which cannot form such strong interactions.

Structural Effects on Boiling Point

The structure of a molecule, including its shape and the presence of substituents, affects its boiling point. For example, cyclic structures may have different steric effects compared to acyclic ones. In the given compounds, the presence of a nitrogen atom in a cyclic structure versus a nitrogen atom with a methyl group can lead to differences in boiling point due to variations in molecular interactions and steric hindrance.

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Related Practice

Textbook Question

Predict which compound in each pair has the higher boiling point. Explain your prediction.

(a) CH₃CH₂OCH₃ or CH₃CH(OH)CH₃

(b) CH₃CH₂CH₂CH₃ or CH₃CH₂CH₂CH₂CH₃

Textbook Question

Which of the following pure compounds can form hydrogen bonds? Which can form hydrogen bonds with water? Which ones do you expect to be soluble in water?

e. CH₃(CH₂)₃CH₃

f. CH₂=CH—CH₂CH₃

g. CH₃COCH₃

h. CH₃CH₂COOH

Textbook Question

Draw the hydrogen bonding that takes place between

a. two molecules of ethanol.

b. two molecules of propylamine.

Textbook Question

For each pair of compounds, circle the compound you expect to have the higher boiling point. Explain your reasoning.

a. (CH3)3C—C(CH₃)₃ or (CH₃)₂CH—CH₂CH₂—CH(CH₃)₂

b. CH₃(CH₂)₆CH₃ or CH₃(CH₂)₅CH₂OH

c. CH₃CH₂OCH₂CH₃ or CH₃CH₂CH₂CH₂OH

Textbook Question

Draw the hydrogen bonding that takes place between

c. a molecule of dimethyl ether and two molecules of water.

d. two molecules of trimethylamine and a molecule of water.

Textbook Question

Diethyl ether and butan-1-ol are isomers, and they have similar solubilities in water. Their boiling points are very different, however. Explain why these two compounds have similar solubility properties but dramatically different boiling points.

Textbook Question

N-Methylpyrrolidine has a boiling point of 81 °C, and piperidine has a boiling point of 106 °C.

b. Tetrahydropyran has a boiling point of 88 °C, and cyclopentanol has a boiling point of 141 °C. These two isomers have a boiling point difference of 53 °C. Explain why the two oxygen-containing isomers have a much larger boiling point difference than the two amine isomers.

Textbook Question

List each set of compounds in order of increasing boiling point.

a. hexane, octane, and decane

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