Textbook Question
The effectiveness of a barbiturate as a sedative is related to its ability to penetrate the nonpolar membrane of a cell. Which of the following barbiturates would you expect to be the more effective sedative?
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Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
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Bruice 8th EditionCh. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and StructureProblem 40b
Bruice 8th EditionCh. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and StructureProblem 40bChapter 4, Problem 40b
Draw a potential-energy diagram for rotation about the C-2---C-3 bond of pentane through 360°, starting with the least stable conformer.
Verified step by step guidance1
Identify the structure of pentane and focus on the C-2-C-3 bond. Pentane is a straight-chain alkane with the molecular formula C5H12. The C-2-C-3 bond is the central bond in the molecule, and rotation about this bond will result in different conformations.
Understand the concept of conformational analysis. As the C-2-C-3 bond rotates, the relative positions of the substituents (hydrogens and methyl groups) change, leading to different levels of steric hindrance and stability. The least stable conformer typically occurs when bulky groups are eclipsed.
Visualize the conformations during rotation. Start with the least stable conformer (eclipsed conformation where the methyl groups on C-2 and C-3 are directly aligned). As the bond rotates, the molecule will pass through staggered and eclipsed conformations, with staggered conformations being more stable due to reduced steric hindrance.
Draw the potential-energy diagram. On the x-axis, represent the dihedral angle of rotation (0° to 360°). On the y-axis, represent the potential energy. Mark the least stable conformer at 0° (highest energy), then show alternating peaks (eclipsed conformations) and valleys (staggered conformations) as the bond rotates through 360°.
Label key points on the diagram. Indicate the dihedral angles corresponding to eclipsed conformations (0°, 120°, 240°, 360°) and staggered conformations (60°, 180°, 300°). Ensure the energy peaks are higher for eclipsed conformations and lower for staggered conformations, with the lowest energy staggered conformation being the anti-conformation (180°).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Conformational Analysis
Conformational analysis involves studying the different spatial arrangements of a molecule that can be interconverted by rotation around single bonds. In the case of pentane, various conformers exist due to the rotation around the C-2-C-3 bond, each with distinct energy levels. Understanding these conformers is essential for predicting stability and reactivity.
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Understanding what a conformer is.
Potential Energy Diagram
A potential energy diagram visually represents the energy changes that occur as a molecule rotates around a bond. The y-axis typically shows potential energy, while the x-axis represents the dihedral angle of rotation. Peaks in the diagram correspond to higher energy, less stable conformers, while valleys indicate lower energy, more stable conformers.
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06:07Introduction to free energy diagrams.
Stability of Conformers
The stability of conformers is influenced by steric interactions and torsional strain. In pentane, certain conformers are more stable due to minimized steric hindrance between bulky groups. Recognizing the least stable conformer at the start of the rotation is crucial for accurately drawing the potential energy diagram and understanding the energy landscape of the molecule.
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03:29Understanding what a conformer is.
Related Practice
Textbook Question
Using Newman projections, draw the most stable conformer for each of the following:
b. 3-methylhexane, viewed along the C-3----C-4 bond
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Textbook Question
Draw all the staggered and eclipsed conformers that result from rotation about the C-2-C-3 bond of pentane.
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Textbook Question
Using Newman projections, draw the most stable conformer for each of the following:
a. 3-methylpentane, viewed along the C-2---C-3 bond
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Textbook Question
In which solvent would cyclohexane have the lowest solubility: 1-pentanol, diethyl ether, ethanol, or hexane?
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Textbook Question
Convert the following Newman projections to skeletal structures and name them.
a.
b.
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