Textbook Question
Draw the most stable conformation of
b. trans-1-tert-butyl-2-methylcyclohexane.
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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 29a,b
Draw the two chair conformations of each of the following substituted cyclohexanes. In each case, label the more stable conformation.
a. cis-1-ethyl-2-methylcyclohexane
b. trans-1,2-diethylcyclohexane
Verified step by step guidance1
Identify the substituents and their positions on the cyclohexane ring for each compound. For cis-1-ethyl-2-methylcyclohexane, the ethyl and methyl groups are on adjacent carbons and on the same side of the ring. For trans-1,2-diethylcyclohexane, the ethyl groups are on adjacent carbons but on opposite sides of the ring.
Draw the basic cyclohexane chair conformation. Remember that cyclohexane can exist in two chair conformations that interconvert through a ring-flip.
For cis-1-ethyl-2-methylcyclohexane, place the ethyl group on carbon 1 and the methyl group on carbon 2. In the first chair conformation, place both substituents in axial positions. In the second chair conformation, perform a ring-flip to place both substituents in equatorial positions.
For trans-1,2-diethylcyclohexane, place one ethyl group on carbon 1 in an axial position and the other ethyl group on carbon 2 in an equatorial position in the first chair conformation. Perform a ring-flip to switch the positions of the ethyl groups, placing the first ethyl group in an equatorial position and the second in an axial position in the second chair conformation.
Evaluate the stability of each conformation by considering steric hindrance. Generally, the conformation with the larger substituents in equatorial positions is more stable due to reduced steric strain. Label the more stable conformation for each compound.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Chair Conformation
Chair conformation is a three-dimensional shape that cyclohexane adopts to minimize steric strain and torsional strain. It resembles a chair, with alternating axial and equatorial positions for substituents. Understanding this conformation is crucial for analyzing the stability of substituted cyclohexanes.
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03:29
Understanding what a conformer is.
Axial and Equatorial Positions
In cyclohexane's chair conformation, substituents can occupy axial positions, which are parallel to the ring's axis, or equatorial positions, which are around the equator of the ring. Equatorial positions are generally more stable due to reduced steric hindrance, making them preferable for larger substituents.
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04:02Equatorial Preference
Cis and Trans Isomerism
Cis and trans isomerism refers to the relative positioning of substituents on a cyclohexane ring. In cis isomers, substituents are on the same side, while in trans isomers, they are on opposite sides. This affects the stability and spatial arrangement of the chair conformations, influencing which conformation is more stable.
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00:44Is the following cyclohexane cis or trans?
Related Practice
Textbook Question
Use your results from Problem 3-27 to complete the following table. Each entry shows the positions of two groups arranged as shown. For example, two groups that are trans on adjacent carbons (trans-1,2) must be both equatorial (e,e) or both axial (a,a).
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Textbook Question
a. Draw both chair conformations of cis-1,4-dimethylcyclohexane, and determine which conformer is more stable.
b. Repeat for the trans isomer.
c. Predict which isomer (cis or trans) is more stable.
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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.
(e)
(f)
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Textbook Question
Draw the most stable conformation of
a. cis-1-tert-butyl-3-ethylcyclohexane.
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Textbook Question
Draw the two chair conformations of each of the following substituted cyclohexanes. In each case, label the more stable conformation.]
c. cis-1-ethyl-4-isopropylcyclohexane
d. trans-1-ethyl-4-methylcyclohexane
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