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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6:23 minutes

Problem 6d,e,f

Textbook Question

For each pair of compounds, circle the compound you expect to have the higher boiling point. Explain your reasoning.
(d) HOCH₂—(CH₂)₄—CH₂OH or (CH₃)₃CCH(OH)CH₃
(e) (CH₃CH₂CH₂)₂NH or (CH₃CH₂)₃N
(f)

Verified step by step guidance

Step 1: Understand the concept of boiling point. Boiling point is the temperature at which a substance transitions from a liquid to a gas. It is influenced by intermolecular forces such as hydrogen bonding, dipole-dipole interactions, and van der Waals forces.

Step 2: Analyze the molecular structure of each compound. For compound d, HOCH2—(CH2)4—CH2OH is a linear diol, while (CH3)3CCH(OH)CH3 is a branched alcohol. Linear molecules generally have stronger van der Waals forces due to greater surface area, potentially leading to higher boiling points.

Step 3: Consider hydrogen bonding. Both compounds in pair d can form hydrogen bonds due to the presence of hydroxyl groups (-OH). However, the linear diol can form more extensive hydrogen bonding networks compared to the branched alcohol, which may increase its boiling point.

Step 4: Examine the nitrogen-containing compounds in pair e. (CH3CH2CH2)2NH is a secondary amine, while (CH3CH2)3N is a tertiary amine. Secondary amines can form hydrogen bonds, whereas tertiary amines cannot, due to the lack of a hydrogen atom bonded to nitrogen. This suggests that the secondary amine may have a higher boiling point.

Step 5: Analyze the image for pair f. The image shows two cyclic amines: one with an NH group and the other with an NH2 group. The NH2 group can form more hydrogen bonds compared to the NH group, potentially leading to a higher boiling point for the compound with the NH2 group.

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Key Concepts

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

Hydrogen Bonding

Hydrogen bonding is a strong type of dipole-dipole interaction that occurs when hydrogen is bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine. This interaction significantly increases the boiling point of a compound because more energy is required to break these bonds during the phase transition from liquid to gas. In the context of the question, compounds with more hydrogen bonding sites will generally have higher boiling points.

Molecular Structure and Surface Area

The molecular structure and surface area of a compound affect its boiling point. Linear or less branched molecules have greater surface area, leading to stronger van der Waals forces, which increase boiling points. In contrast, more compact or branched structures have less surface area, resulting in weaker intermolecular forces and lower boiling points. This concept helps in comparing the boiling points of the given compounds based on their structural differences.

Functional Groups and Polarity

Functional groups in organic molecules influence their polarity and, consequently, their boiling points. Polar functional groups, such as hydroxyl (OH) and amino (NH2) groups, enhance intermolecular attractions like hydrogen bonding, raising the boiling point. In the given question, the presence and type of functional groups in each compound determine their relative boiling points by affecting the overall polarity and intermolecular interactions.

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Related Practice

Textbook Question

Explain why

a. H₂O (100 °C) has a higher boiling point than CH₃OH 165 °C2.

b. H₂O (100 °C) has a higher boiling point than NH₃ (-33 °C).

Textbook Question

Which has

a. the higher boiling point: 1-bromopentane or 1-bromohexane?

b. the higher boiling point: pentyl chloride or isopentyl chloride?

Textbook Question

In Table 7.2, what is the smallest alkane, the smallest terminal alkene, and the smallest terminal alkyne that are liquids at room temperature, which is generally taken to be 20 °C to 25 °C?

Textbook Question

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

c. N,N-Dimethylformamide has a boiling point of 150 °C, and N-methylacetamide has a boiling point of 206 °C, for a difference of 56 °C. Explain why these two nitrogen-containing isomers have a much larger boiling point difference than the two amine isomers. Also explain why these two amides have higher boiling points than any of the other four compounds shown (two amines, an ether, and an alcohol).

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?

a. (CH₃CH₂)₂NH

b. (CH₃CH₂)₃N

c. CH₃CH₂CH₂OH

d. (CH₃CH₂CH₂)₂OH

Textbook Question

Contrary to expectation, the addition of more fluorines to ethane lowers the boiling point. Explain this phenomenon.

Textbook Question

In each pair, choose the compound you would expect to have the highest boiling/melting point.

(b)

Multiple Choice

Which of these phenomena result from hydrogen bonding?

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