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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4:33 minutes

Problem 50c

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: Axial substituents experience 1,3-diaxial interactions, which are steric clashes with hydrogen atoms on the same side of the ring. Equatorial substituents are generally more stable because they avoid these interactions.

Examine the cis-1-ethyl-2-methylcyclohexane: In the cis isomer, both substituents (ethyl and methyl) 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 the axial substituent's 1,3-diaxial interactions.

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

Compare the stability: The trans isomer is more stable than the cis isomer because it allows both substituents to occupy equatorial positions, 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 cycloalkanes, '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 compound.

Steric Strain

Steric strain arises when atoms are forced closer together than their preferred distance, leading to increased energy and decreased stability. In cyclohexane derivatives, steric strain can occur when bulky groups are positioned near each other, making the molecule less stable. Understanding steric interactions is crucial for predicting the stability of isomers.

Chair Conformation

The chair conformation is the most stable arrangement of cyclohexane, minimizing steric strain and torsional strain. In this conformation, substituents can occupy equatorial or axial positions, with equatorial positions generally being more stable for larger groups. Analyzing the chair conformations of cis and trans isomers helps determine their relative stability.

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Related Practice

Textbook Question

For each structure shown, draw the two chair conformations and choose which is most stable. Be sure that your second chair is the flipped version of the first. [Make sure that wedged substituents are up in the chair, regardless of whether up is equatorial or axial.]

(g)

Textbook Question

Draw the two chair conformers for each of the following and indicate which conformer is more stable:

b. trans-1-ethyl-2-methylcyclohexane

Textbook Question

Draw the two chair conformers for each of the following and indicate which conformer is more stable: