Textbook Question
Ionic compounds like sodium acetate have a high melting point. Despite this, they are highly soluble in water. Why?
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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 73
Mullins 1st EditionCh. 3 - Alkanes and Cycloalkanes: Properties and Conformational AnalysisProblem 73Chapter 2, Problem 73
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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Consider the molecular structures of methylcyclohexane and toluene. Methylcyclohexane is a saturated hydrocarbon (alkane) with a cyclohexane ring and a methyl group attached, while toluene is an aromatic compound with a benzene ring and a methyl group attached.
Analyze the intermolecular forces present in each molecule. Methylcyclohexane primarily exhibits London dispersion forces, which are relatively weak and depend on molecular size and shape. Toluene, on the other hand, has stronger π-π interactions due to the aromatic benzene ring.
Understand how molecular shape affects packing efficiency in the solid state. Toluene's flat, planar aromatic structure allows for better stacking and closer packing in the solid phase, which increases the melting point. Methylcyclohexane's non-planar, bulky structure reduces packing efficiency.
Consider the role of molecular weight. While methylcyclohexane has a slightly higher molecular weight, melting point is more influenced by intermolecular forces and molecular packing rather than molecular weight alone.
Conclude that the higher melting point of toluene is due to its stronger intermolecular forces (π-π interactions) and more efficient molecular packing in the solid state compared to methylcyclohexane.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Molecular Weight vs. Melting Point
Molecular weight is the sum of the atomic weights of all atoms in a molecule, but it does not directly correlate with melting point. Melting point is influenced by intermolecular forces, such as hydrogen bonding, dipole-dipole interactions, and London dispersion forces. Thus, a compound with a higher molecular weight may not necessarily have a higher melting point if its intermolecular interactions are weaker.
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Molecular Shape and Interactions
The shape of a molecule affects how closely molecules can pack together, influencing their physical properties. Toluene, being a more symmetrical and planar molecule, can stack more efficiently than the bulky methylcyclohexane. This efficient packing leads to stronger van der Waals forces in toluene, contributing to its higher melting point despite its lower molecular weight.
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Intermolecular Forces
Intermolecular forces are the forces of attraction between molecules, which play a crucial role in determining physical properties like melting and boiling points. Toluene exhibits stronger dipole-dipole interactions due to its polar C-H bonds, while methylcyclohexane's interactions are primarily due to weaker London dispersion forces. The strength and type of these forces significantly influence the melting behavior of the substances.
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Related Practice
Textbook Question
Identify the mistakes contained within the following structures.
(a)
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Textbook Question
Correct the following incorrect names using standard IUPAC nomenclature. [Draw a compound that corresponds to the incorrect name, and then rename it.]
(d) 4-butyldecane
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Textbook Question
Identify the functional groups in each of the following molecules. [The number of functional groups has been given to assist you.]
(a) [Three]
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Textbook Question
Identify the functional groups in each of the following molecules. [The number of functional groups has been given to assist you.]
(b) [Two]
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Textbook Question
Correct the following incorrect names using standard IUPAC nomenclature. [Draw a compound that corresponds to the incorrect name, and then rename it.]
(e) 2,6-diethyl-1-methylcycloheptane
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