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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4:44 minutes

Problem 8b

Textbook Question

Choose the molecule in each pair you'd expect to have the higher boiling point. Explain your reasoning.
(b)

Verified step by step guidance

Step 1: Understand the factors that influence boiling points. Boiling points are primarily affected by intermolecular forces, molecular weight, and molecular structure. Stronger intermolecular forces (e.g., hydrogen bonding, dipole-dipole interactions, and London dispersion forces) lead to higher boiling points.

Step 2: Identify the types of intermolecular forces present in each molecule of the pair. For example, check if the molecules can form hydrogen bonds (e.g., presence of -OH or -NH groups), have polar bonds (dipole-dipole interactions), or are nonpolar (relying on London dispersion forces).

Step 3: Compare the molecular weights of the two molecules. If the intermolecular forces are similar, the molecule with the higher molecular weight will generally have a higher boiling point due to increased London dispersion forces.

Step 4: Consider the molecular structure. Linear molecules tend to have higher boiling points than branched molecules of similar molecular weight because they have a larger surface area for intermolecular interactions.

Step 5: Based on the analysis of intermolecular forces, molecular weight, and structure, determine which molecule in the pair has the higher boiling point and explain your reasoning clearly.

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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. The main types include hydrogen bonding, dipole-dipole interactions, and London dispersion forces. Molecules with stronger intermolecular forces generally have higher boiling points because more energy is required to separate them during the phase change from liquid to gas.

Molecular Weight

Molecular weight, or molar mass, refers to the mass of a molecule based on the sum of the atomic weights of its constituent atoms. Generally, larger molecules with higher molecular weights exhibit higher boiling points due to increased London dispersion forces, which arise from temporary dipoles that occur in larger electron clouds. Thus, comparing molecular weights can provide insight into boiling point trends.

Polarity

Polarity describes the distribution of electrical charge over the atoms in a molecule. Polar molecules have a significant difference in electronegativity between bonded atoms, leading to dipole moments. Polar molecules typically have higher boiling points than nonpolar molecules of similar size due to stronger dipole-dipole interactions, which require more energy to overcome during boiling.

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Textbook Question

In each pair of compounds, which compound has the higher boiling point? Explain your reasoning.

c. 2,2,5-trimethylhexane or nonane

Textbook Question

In each pair of compounds, which compound has the higher boiling point? Explain your reasoning.

b. nonane or 2-methylheptane

Textbook Question

In each pair of compounds, which compound has the higher boiling point? Explain your reasoning.

a. octane or 2,2,3-trimethylpentane

Textbook Question

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

b. Octane, (CH₃)₃C—C(CH₃)₃ and CH₃CH₂C(CH₃)₂CH₂CH₂CH₃

Textbook Question

Ionic compounds like sodium acetate have a high melting point. Despite this, they are highly soluble in water. Why?

Textbook Question

Despite methylcyclohexane (98.2 amu) having a higher molecular weight than toluene (92.1 amu), toluene melts at a higher temperature. Why? [Think about how the molecules can interact with each other based on their shape.]

Textbook Question

Choose the molecule in each pair you'd expect to have the higher boiling point. Explain your reasoning.

(a) eicosane ( C₂₀H₄₂) vs pentadecane

Textbook Question

Draw a picture of the hydrogen bonding in methanol.

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