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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4:50 minutes

Problem 42a

Textbook Question

In each pair of compounds, which compound has the higher boiling point? Explain your reasoning.
a. octane or 2,2,3-trimethylpentane

Verified step by step guidance

Identify the structural differences between octane and 2,2,3-trimethylpentane. Octane is a straight-chain alkane with the formula C₈H₁₈, while 2,2,3-trimethylpentane is a branched alkane with the formula C₈H₁₈.

Understand the impact of molecular structure on boiling points. Straight-chain alkanes generally have higher boiling points than their branched counterparts due to increased surface area, which enhances van der Waals forces.

Consider the van der Waals forces. These are intermolecular forces that depend on the surface area of the molecule. A larger surface area in straight-chain alkanes allows for stronger van der Waals forces, leading to higher boiling points.

Analyze the branching in 2,2,3-trimethylpentane. The presence of branches reduces the surface area available for intermolecular interactions, thus decreasing the boiling point compared to a straight-chain alkane of the same molecular weight.

Conclude that octane, being a straight-chain alkane, will have a higher boiling point than 2,2,3-trimethylpentane due to stronger van der Waals forces resulting from its larger surface area.

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Key Concepts

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

Boiling Point

The boiling point of a compound is the temperature at which its vapor pressure equals the atmospheric pressure, causing it to transition from liquid to gas. It is influenced by molecular weight, intermolecular forces, and molecular structure. Stronger intermolecular forces, such as hydrogen bonding or van der Waals forces, typically result in higher boiling points.

Intermolecular Forces

Intermolecular forces are the forces that hold molecules together, affecting properties like boiling point and solubility. In hydrocarbons, van der Waals forces (dispersion forces) are predominant. Linear molecules, like octane, have stronger dispersion forces due to greater surface area contact compared to branched molecules, leading to higher boiling points.

Molecular Structure

Molecular structure refers to the arrangement of atoms within a molecule, impacting its physical properties. Linear structures, such as octane, allow for more efficient packing and stronger intermolecular interactions than branched structures like 2,2,3-trimethylpentane. This structural difference often results in higher boiling points for linear molecules.

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Related Practice

Textbook Question

Explain why

c. H₂O (100 °C) has a higher boiling point than HF 120 °C2.

d. HF 120 °C2 has a higher boiling point than NH₃ (-33 °C).

Textbook Question

Which of the following compounds forms hydrogen bonds between its molecules?

1. CH₃CH₂OCH₂CH₂OH

2. CH₃CH₂N(CH₃)₂

3. CH₃CH₂CH₂CH₂Br

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

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

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

Textbook Question

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

(b)

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.]

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In each pair of compounds, which compound has the higher boiling point? Explain your reasoning. a. octane or 2,2,3-trimethylpentane

Key Concepts

Boiling Point

Intermolecular Forces

Molecular Structure

Watch next

In each pair of compounds, which compound has the higher boiling point? Explain your reasoning.
a. octane or 2,2,3-trimethylpentane