Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

4. Alkanes and Cycloalkanes

Equatorial Preference

Organic Chemistry

4. Alkanes and Cycloalkanes

Equatorial Preference

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5:43 minutes

Problem 50(c)

Textbook Question

Which compound is more stable: cis-1-ethyl-2-methylcyclohexane or trans-1-ethyl-2-methylcyclohexane?

Verified step by step guidance

Analyze the structure of cyclohexane: Cyclohexane adopts a chair conformation to minimize steric strain and torsional strain. Substituents on the cyclohexane ring can occupy either axial (parallel to the ring's axis) or equatorial (perpendicular to the ring's axis) positions.

Understand the steric interactions: Larger substituents prefer the equatorial position because it minimizes 1,3-diaxial interactions, which are steric clashes between axial substituents on the same side of the ring.

Examine the cis isomer: In cis-1-ethyl-2-methylcyclohexane, the ethyl and methyl groups are on the same side of the ring. One substituent will occupy an axial position, and the other will occupy an equatorial position in the chair conformation. This arrangement leads to steric strain due to 1,3-diaxial interactions for the axial substituent.

Examine the trans isomer: In trans-1-ethyl-2-methylcyclohexane, the ethyl and methyl groups are on opposite sides of the ring. Both substituents can occupy equatorial positions in the chair conformation, minimizing steric strain and 1,3-diaxial interactions.

Compare the stability: The trans isomer is more stable than the cis isomer because both substituents can adopt equatorial positions in the trans isomer, reducing steric strain. In contrast, the cis isomer forces one substituent into the less favorable axial position, increasing steric strain.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Cis-Trans Isomerism

Cis-trans isomerism refers to the different spatial arrangements of atoms in a molecule. In the context of cyclohexane derivatives, 'cis' indicates that substituents are on the same side of the ring, while 'trans' means they are on opposite sides. This arrangement significantly affects the steric interactions and overall stability of the molecule.

Steric Hindrance

Steric hindrance occurs when atoms in a molecule are forced close together, leading to increased repulsion between electron clouds. In cyclohexane derivatives, bulky groups can create steric strain when positioned near each other. Understanding steric hindrance is crucial for predicting the stability of different isomers, as it influences the energy and conformation of the molecule.

Cyclohexane Conformation

Cyclohexane can adopt various conformations, with the chair conformation being the most stable due to minimized steric strain. The positioning of substituents in these conformations affects the overall stability of the compound. In comparing cis and trans isomers, the ability of substituents to occupy equatorial versus axial positions in the chair form is key to determining which isomer is more stable.

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