Textbook Question
Choose the molecule in each pair you'd expect to have the higher boiling point. Explain your reasoning.
(b)
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Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471
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Table of contents
- Ch. 2 - General Chemistry Translated: Finding the Electrons114
- Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis109
- Ch. 4 - Acids and Bases: Electron Flow144
- Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics118
- Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space112
- Ch. 7 - Principles of Green (Organic) Chemistry3
- Ch. 8 - Alkenes I: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes II: Oxidation and Reduction150
- Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions101
- Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions108
- Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes172
- Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination239
- Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems I: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems II: Pericyclic Reactions54
- Ch. 23 - Benzene I: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring62
- Ch. 25 - Amines: Structure, Reactions, and Synthesis27
- Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis9
- Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids54
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
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Mullins 1st EditionCh. 3 - Alkanes and Cycloalkanes: Properties and Conformational AnalysisProblem 8a
Mullins 1st EditionCh. 3 - Alkanes and Cycloalkanes: Properties and Conformational AnalysisProblem 8aChapter 2, Problem 8a
Choose the molecule in each pair you'd expect to have the higher boiling point. Explain your reasoning.
(a) eicosane ( C20H42) vs pentadecane
Verified step by step guidance1
Step 1: Understand the relationship between molecular size and boiling point. Larger molecules generally have higher boiling points due to increased van der Waals forces (London dispersion forces) between molecules.
Step 2: Compare the molecular structures of eicosane (C₂₀H₄₂) and pentadecane (C₁₅H₃₂). Eicosane has 20 carbon atoms, while pentadecane has 15 carbon atoms. The larger molecular size of eicosane results in stronger intermolecular forces.
Step 3: Consider the surface area of the molecules. Eicosane, being larger, has a greater surface area, which enhances the strength of London dispersion forces compared to pentadecane.
Step 4: Analyze the boiling point trend in alkanes. As the number of carbon atoms increases, the boiling point increases due to the cumulative effect of stronger intermolecular forces.
Step 5: Conclude that eicosane (C₂₀H₄₂) is expected to have a higher boiling point than pentadecane (C₁₅H₃₂) based on its larger molecular size and stronger intermolecular forces.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Boiling Point and Molecular Weight
The boiling point of a substance is influenced by its molecular weight; generally, larger molecules have higher boiling points due to increased van der Waals forces. In this case, eicosane (C₂₀H₄₂) has a higher molecular weight than pentadecane (C₁₅H₃₂), suggesting it will have a higher boiling point.
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Intermolecular Forces
Intermolecular forces, particularly London dispersion forces, play a crucial role in determining boiling points. Larger hydrocarbons have more surface area, leading to stronger dispersion forces, which require more energy (heat) to overcome, resulting in higher boiling points for larger molecules.
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Structural Isomerism
Structural isomerism refers to compounds with the same molecular formula but different structural arrangements. In the context of boiling points, isomers can exhibit different boiling points due to variations in their shapes and the resulting differences in intermolecular interactions, although this is less relevant when comparing straight-chain alkanes like eicosane and pentadecane.
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Related Practice
Textbook Question
How many hydrogens would you expect a 24-carbon compound from each of the following molecular classes to have?
(c) Alkyne
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Textbook Question
How many hydrogens would you expect a 24-carbon compound from each of the following molecular classes to have?
(b) Alkene
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Textbook Question
Rank the following molecules from least water soluble to most water soluble. Explain your reasoning.
(b) LiCl
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Textbook Question
Rank the following molecules from least water soluble to most water soluble. Explain your reasoning.
(a) H3C ― OH
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Textbook Question
Draw the molecular orbital picture for propane. Your picture should clearly show the shape and hybridization of the carbons. Label all σ bonds.
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