Textbook Question
Convert each Newman projection to the equivalent line–angle formula, and assign the IUPAC name.
(c)
(d)
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Ch.3 - Structure and Stereochemistry of Alkanes
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 3, Problem 50
Conformational studies on ethane-1,2-diol (HOCH2–CH2OH) have shown the most stable conformation about the central C―C bond to be the gauche conformation, which is 9.6 kJ/mol (2.3 kcal/mol) more stable than the anti conformation. Draw Newman projections of these conformers, and explain this curious result.
Verified step by step guidance1
Begin by understanding the structure of ethane-1,2-diol (HOCH2—CH2OH). It consists of two carbon atoms connected by a single bond, with each carbon atom also bonded to a hydroxyl group (OH) and hydrogen atoms.
To draw the Newman projection, imagine looking straight down the C—C bond. In the anti conformation, the two hydroxyl groups (OH) are positioned 180 degrees apart, minimizing steric hindrance but not taking advantage of any potential stabilizing interactions.
In the gauche conformation, the hydroxyl groups are positioned 60 degrees apart. This proximity allows for the possibility of intramolecular hydrogen bonding between the OH groups, which can stabilize the molecule.
Draw the Newman projection for the anti conformation: the front carbon will have one OH group pointing up and the other substituents (hydrogens) staggered around it. The back carbon will have its OH group pointing down, directly opposite the front OH group.
Draw the Newman projection for the gauche conformation: the front carbon will have one OH group pointing up and the other substituents staggered. The back carbon will have its OH group positioned 60 degrees from the front OH group, allowing for potential hydrogen bonding, which explains the increased stability of the gauche conformation.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Newman Projection
A Newman projection is a way of visualizing the conformation of a molecule from a specific angle, looking down the axis of a bond. It helps in understanding the spatial arrangement of atoms around a bond, particularly useful for analyzing conformations in alkanes. In the case of ethane-1,2-diol, it allows us to compare the spatial orientation of the hydroxyl groups in different conformations.
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00:34
Introduction to Drawing Newman Projections
Gauche and Anti Conformations
Gauche and anti are terms used to describe the relative positions of substituents around a single bond in a molecule. In a gauche conformation, substituents are 60 degrees apart, while in an anti conformation, they are 180 degrees apart. For ethane-1,2-diol, the gauche conformation is more stable due to favorable interactions between the hydroxyl groups, despite the typical steric hindrance associated with such proximity.
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Hydrogen Bonding
Hydrogen bonding is a type of dipole-dipole interaction that occurs between a hydrogen atom bonded to a highly electronegative atom (like oxygen) and another electronegative atom. In ethane-1,2-diol, the gauche conformation allows for intramolecular hydrogen bonding between the hydroxyl groups, which stabilizes this conformation over the anti conformation, where such interactions are not possible.
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Related Practice
Textbook Question
The most stable form of the common sugar glucose contains a six-membered ring in the chair conformation with all the substituents equatorial. Draw this most stable conformation of glucose.
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Textbook Question
This is a Newman projection of a substituted cyclohexane.
b. Draw the equivalent structure using wedge and dash notation on a cyclohexane hexagon.
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Textbook Question
Draw Newman projections along the C3―C4 bond to show the most stable and least stable conformations of 3-ethyl-2,4,4-trimethylheptane.
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Textbook Question
This is a Newman projection of a substituted cyclohexane. a. Draw the equivalent chair form.
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Textbook Question
Convert each Newman projection to the equivalent line–angle formula, and assign the IUPAC name. g.
(g)
(h)
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