Textbook Question
Draw 1,2,3,4,5,6-hexamethylcyclohexane with all the methyl groups
b. in equatorial positions.
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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 25a
Draw the most stable conformation of
a. ethylcyclohexane.
Verified step by step guidance1
Start by understanding the structure of cyclohexane. Cyclohexane is a six-membered ring that can adopt different conformations, with the chair conformation being the most stable due to minimized steric strain and torsional strain.
Identify the substituent group in ethylcyclohexane, which is the ethyl group (C₂H₅). This group will be attached to one of the carbon atoms in the cyclohexane ring.
Consider the chair conformation of cyclohexane. In this conformation, each carbon atom has two positions for substituents: axial (pointing up or down, perpendicular to the ring) and equatorial (pointing outwards, parallel to the ring).
Place the ethyl group in the equatorial position on the cyclohexane ring. This position is preferred for larger groups like ethyl because it minimizes steric hindrance and is more stable than the axial position.
Draw the complete structure of ethylcyclohexane in the chair conformation with the ethyl group in the equatorial position. Ensure that the hydrogen atoms are appropriately placed in axial and equatorial positions to complete the conformation.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Cyclohexane Conformations
Cyclohexane can adopt several conformations, with the chair conformation being the most stable due to minimized steric strain and torsional strain. In the chair form, carbon atoms are staggered, reducing repulsion between hydrogen atoms. Understanding these conformations is crucial for predicting the stability of substituted cyclohexanes.
Recommended video:
Guided course
03:29
Understanding what a conformer is.
Axial and Equatorial Positions
In the chair conformation of cyclohexane, substituents can occupy axial or equatorial positions. Axial positions are perpendicular to the ring plane, while equatorial positions are parallel. Substituents prefer equatorial positions to minimize steric hindrance, which is key to determining the most stable conformation of substituted cyclohexanes like ethylcyclohexane.
Recommended video:
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04:02Equatorial Preference
Steric Hindrance
Steric hindrance occurs when atoms or groups are too close, causing repulsion and destabilizing the molecule. In cyclohexane derivatives, larger groups in axial positions experience more steric hindrance due to 1,3-diaxial interactions. Placing bulky groups like ethyl in equatorial positions reduces steric strain, leading to a more stable conformation.
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02:53Understanding steric effects.
Related Practice
Textbook Question
Draw the most stable conformation of
c. cis-1-tert-butyl-4-isopropylcyclohexane.
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Textbook Question
Draw the most stable conformation of
b. 3-isopropyl-1,1-dimethylcyclohexane.
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Textbook Question
Table 3-6 shows that the axial–equatorial energy difference for methyl, ethyl, and isopropyl groups increases gradually: 7.6, 7.9, and 8.8 kJ/mol (1.8, 1.9, and 2.1 kcal/mol). The tert-butyl group jumps to an energy difference of 23 kJ/mol (5.4 kcal/mol), over twice the value for the isopropyl group. Draw pictures of the axial conformations of isopropylcyclohexane and tert-butylcyclohexane, and explain why the tert-butyl substituent experiences such a large increase in axial energy over the isopropyl group.
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Textbook Question
Draw a Newman projection, similar to Figure 3-25 down the C1—C6 bond in the equatorial conformation of methylcyclohexane. Show that the equatorial methyl group is also anti to C5. (Using your models will help.)
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Textbook Question
Name the following compounds. Remember that two up bonds are cis; two down bonds are cis; one up bond and one down bond are trans.
(c)
(d)
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