Ch.3 - Structure and Stereochemistry of Alkanes

Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook

Wade 9th Edition

Ch.3 - Structure and Stereochemistry of Alkanes

Problem 30a

Chapter 3, Problem 30a

Draw the most stable conformation of
a. cis-1-tert-butyl-3-ethylcyclohexane.

Verified step by step guidance

Begin by understanding the structure of cyclohexane. Cyclohexane can adopt several conformations, with the chair conformation being the most stable due to minimized steric strain and torsional strain.

Identify the substituents on the cyclohexane ring. In this case, we have a tert-butyl group and an ethyl group. The tert-butyl group is larger and will have a greater impact on the stability of the conformation.

Since the compound is cis-1-tert-butyl-3-ethylcyclohexane, both substituents are on the same side of the cyclohexane ring. In the chair conformation, this means they will both be either axial or equatorial.

To achieve the most stable conformation, place the larger tert-butyl group in the equatorial position to minimize steric hindrance. The ethyl group should also be placed in the equatorial position to maintain the cis relationship and further reduce steric strain.

Draw the cyclohexane ring in the chair conformation, ensuring that both the tert-butyl and ethyl groups are equatorial. This arrangement will provide the most stable conformation for cis-1-tert-butyl-3-ethylcyclohexane.

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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. Understanding the chair conformation is crucial for determining the stability of substituted cyclohexanes, as it allows for the analysis of axial and equatorial positions of substituents.

Axial and Equatorial Positions

In the chair conformation of cyclohexane, substituents can occupy axial or equatorial positions. Equatorial positions are generally more stable for bulky groups due to reduced steric hindrance. Identifying the positions of substituents like tert-butyl and ethyl groups is essential for determining the most stable conformation of a substituted cyclohexane.

Cis Configuration

Cis configuration refers to the arrangement where two substituents are on the same side of the cyclohexane ring. This affects the spatial arrangement and stability of the molecule. In cis-1-tert-butyl-3-ethylcyclohexane, both groups must be positioned on the same side, influencing which positions (axial or equatorial) they can occupy in the most stable conformation.

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Related Practice

Textbook Question

Draw the most stable conformation of

b. trans-1-tert-butyl-2-methylcyclohexane.

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Textbook Question

Draw the most stable conformation of

c. trans-1-tert-butyl-3-(1,1-dimethylpropyl)cyclohexane.

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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

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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Textbook Question

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