Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure

Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook

Bruice 8th Edition

Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure

Problem 74d

Chapter 4, Problem 74d

Draw the two chair conformers for each of the following and indicate which conformer is more stable:
d. cis-1,2-diethylcyclohexane

Verified step by step guidance

Step 1: Begin by understanding the structure of cyclohexane and its chair conformations. Cyclohexane can adopt two chair conformations, which are interconvertible through a ring flip. Each carbon atom in the chair conformation has two substituent positions: axial (pointing up or down, perpendicular to the ring) and equatorial (pointing outward, roughly parallel to the ring plane).

Step 2: Analyze the substituents in cis-1,2-diethylcyclohexane. The 'cis' designation means that both ethyl groups are on the same side of the ring. Assign the substituents to positions on adjacent carbons in the chair conformation, ensuring they are both either axial or equatorial to maintain the cis relationship.

Step 3: Draw the first chair conformer. Place one ethyl group in the axial position on carbon 1 and the other ethyl group in the axial position on carbon 2. Ensure the cis relationship is preserved by keeping both substituents on the same side of the ring.

Step 4: Draw the second chair conformer by performing a ring flip. In this conformer, the ethyl group on carbon 1 will move to the equatorial position, and the ethyl group on carbon 2 will also move to the equatorial position. Again, ensure the cis relationship is maintained.

Step 5: Compare the stability of the two conformers. Substituents in the equatorial position experience less steric hindrance compared to axial positions. Therefore, the conformer with both ethyl groups in equatorial positions is more stable due to reduced 1,3-diaxial interactions.

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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 representation of cyclohexane that minimizes steric strain and torsional strain. In this conformation, the carbon atoms are arranged in a staggered manner, allowing for more stable interactions between substituents. Understanding chair conformations is crucial for analyzing the stability of cyclohexane derivatives, as different substituents can occupy axial or equatorial positions, affecting overall stability.

Cis and Trans Isomerism

Cis and trans isomerism refers to the spatial arrangement of substituents around a cyclohexane ring. In cis isomers, substituents are on the same side of the ring, while in trans isomers, they are on opposite sides. This arrangement significantly influences the steric interactions between substituents, which in turn affects the stability of the conformers. For cis-1,2-diethylcyclohexane, both ethyl groups will be on the same side, impacting their positioning in the chair conformations.

Stability of Conformers

The stability of chair conformers is determined by the positioning of substituents in axial or equatorial orientations. Equatorial positions are generally more stable due to reduced steric hindrance and torsional strain compared to axial positions, where substituents can experience 1,3-diaxial interactions. When analyzing the stability of cis-1,2-diethylcyclohexane, it is essential to compare the steric effects of the ethyl groups in both chair conformers to determine which is more stable.

Draw the two chair conformers for each of the following and indicate which conformer is more stable: d. cis-1,2-diethylcyclohexane