Textbook Question
Dimethylamine, (CH3)2NH, has a molecular weight of 45 and a boiling point of 7.4 °C. Trimethylamine, (CH3)3N, has a higher molecular weight (59) but a lower boiling point (3.5 °C). Explain this apparent discrepancy.
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Ch.10 - Structure and Synthesis of Alcohols
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 10, Problem 5
Predict which member of each pair will be more soluble in water. Explain the reasons for your answers.
(a) hexan-1-ol or cyclohexanol
(b) heptan-1-ol or 4-methylphenol
(c) 3-ethylhexan-3-ol or octan-2-ol
(d) hexan-2-ol or cyclooctane-1,4-diol
(e) 
Verified step by step guidance1
Step 1: Solubility in water is influenced by the ability of a molecule to form hydrogen bonds with water. Molecules with polar functional groups, such as hydroxyl (-OH) groups, are more likely to form hydrogen bonds and thus are more soluble in water.
Step 2: For part (a), compare hexan-1-ol and cyclohexanol. Hexan-1-ol has a linear structure, while cyclohexanol is cyclic. The linear structure of hexan-1-ol allows for better interaction with water molecules, but cyclohexanol's compact structure may reduce solubility slightly. Both have one hydroxyl group, so solubility differences will be minor.
Step 3: For part (b), compare heptan-1-ol and 4-methylphenol. Heptan-1-ol has a single hydroxyl group on a linear chain, while 4-methylphenol has an aromatic ring with a hydroxyl group. The aromatic ring in 4-methylphenol contributes to hydrophobicity, making it less soluble in water compared to heptan-1-ol.
Step 4: For part (c), compare 3-ethylhexan-3-ol and octan-2-ol. Both molecules have hydroxyl groups, but 3-ethylhexan-3-ol has branching near the hydroxyl group, which can hinder hydrogen bonding with water. Octan-2-ol has a more linear structure, which may enhance its solubility in water.
Step 5: For part (d) and (e), compare hexan-2-ol and cyclooctane-1,4-diol, and the two structures in the image. Cyclooctane-1,4-diol has two hydroxyl groups, increasing its ability to form hydrogen bonds with water, making it more soluble than hexan-2-ol. Similarly, in part (e), the molecule with two hydroxyl groups will be more soluble in water due to increased hydrogen bonding compared to the molecule with no hydroxyl groups.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Polarity and Solubility
Polarity refers to the distribution of electrical charge over the atoms in a molecule. Polar molecules, which have a significant difference in electronegativity between atoms, tend to dissolve well in polar solvents like water. Understanding the polarity of the functional groups in the compounds, such as hydroxyl (-OH) groups, is crucial for predicting their solubility in water.
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07:13
Functional Classification
Hydrogen Bonding
Hydrogen bonding is a type of intermolecular force that occurs when a hydrogen atom covalently bonded to a highly electronegative atom, like oxygen, interacts with another electronegative atom. Compounds with hydroxyl groups can form hydrogen bonds with water, enhancing their solubility. The ability to form these bonds is a key factor in determining which compound will be more soluble.
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00:48The definition of hydrogenation.
Hydrophobic vs. Hydrophilic Interactions
Hydrophobic interactions occur between nonpolar molecules that do not interact favorably with water, while hydrophilic interactions involve polar molecules that can interact with water. In organic compounds, the presence of long hydrocarbon chains can make a molecule more hydrophobic, reducing its solubility in water. Understanding the balance between hydrophobic and hydrophilic parts of a molecule is essential for predicting solubility.
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Related Practice
Textbook Question
For each molecular formula, draw all the possible constitutional isomers of alcohols with that formula. Give the IUPAC name for each alcohol.
(d) C3H4O
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Textbook Question
Predict which member of each pair will be more acidic. Explain your answers.
d. 2,2-dichloropropan-1-ol or 2,2-difluoropropan-1-ol
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Textbook Question
Give a systematic (IUPAC) name for each diol
(d)
(e)
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Textbook Question
Give a systematic (IUPAC) name for each diol
(a) CH3CH(OH)(CH2)4CH(OH)C(CH3)3
(b) HO-(CH2)8-OH
(c)
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Textbook Question
Predict which member of each pair will be more acidic. Explain your answers.
c. 2-chloroethanol or 2,2-dichloroethanol
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