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

Previous problemNext problem

2:47 minutes

Problem 24

Textbook Question

Table 3-6 shows that the axial–equatorial energy difference for methyl, ethyl, and isopropyl groups increases gradually: 7.6, 7.9, and 8.8 kJ/mol (1.8, 1.9, and 2.1 kcal/mol). The tert-butyl group jumps to an energy difference of 23 kJ/mol (5.4 kcal/mol), over twice the value for the isopropyl group. Draw pictures of the axial conformations of isopropylcyclohexane and tert-butylcyclohexane, and explain why the tert-butyl substituent experiences such a large increase in axial energy over the isopropyl group.

Verified step by step guidance

To draw the axial conformation of isopropylcyclohexane, start by sketching a cyclohexane chair conformation. Place the isopropyl group on one of the axial positions, which are perpendicular to the plane of the ring.

For tert-butylcyclohexane, similarly draw a cyclohexane chair conformation and place the tert-butyl group in an axial position. The tert-butyl group is larger and bulkier than the isopropyl group.

The axial position in a cyclohexane chair conformation is less stable for larger groups due to steric hindrance and 1,3-diaxial interactions. These interactions occur between the axial substituent and the hydrogen atoms on the same side of the ring.

The tert-butyl group experiences a larger increase in axial energy compared to the isopropyl group because it is bulkier, leading to greater steric hindrance and more significant 1,3-diaxial interactions.

The energy difference between axial and equatorial positions is much larger for tert-butyl groups because the equatorial position allows the bulky group to avoid steric clashes, making it significantly more stable than the axial position.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

Key Concepts

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

Axial and Equatorial Positions

In cyclohexane, substituents can occupy two distinct positions: axial and equatorial. Axial substituents are oriented perpendicular to the plane of the ring, while equatorial substituents extend outward, parallel to the plane. The stability of these positions varies, with equatorial generally being more stable due to reduced steric hindrance and torsional strain.

Steric Hindrance

Steric hindrance refers to the repulsion between atoms that occurs when they are brought close together, particularly in bulky groups. In the context of cyclohexane, larger substituents like tert-butyl experience significant steric hindrance when in the axial position, leading to increased energy and instability compared to smaller groups like isopropyl, which can fit more comfortably in the axial position.

Energy Differences in Conformations

The energy difference between axial and equatorial conformations is quantified in kJ/mol or kcal/mol. This difference arises from the steric interactions and torsional strain experienced by substituents in the axial position. For example, the tert-butyl group has a much larger energy difference due to its size, resulting in a more significant preference for the equatorial position compared to smaller groups like isopropyl.

Watch next

Master Equatorial Preference with a bite sized video explanation from Johnny

Start learning

Related Videos

Related Practice

Textbook Question

Draw the most stable conformation of

a. ethylcyclohexane.

Textbook Question

Draw the two chair conformations of each compound, and label the substituents as axial and equatorial. In each case, determine which conformation is more stable.

c. cis-1-ethyl-3-methylcyclohexane

d. trans-1-ethyl-3-methylcyclohexane

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

Textbook Question

The most stable form of the common sugar glucose contains a six-membered ring in the chair conformation with all the substituents equatorial. Draw this most stable conformation of glucose.

Textbook Question

Draw the most stable conformation of

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

Textbook Question

Draw the most stable conformation of

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

Textbook Question

Draw the most stable conformation of

a. cis-1-tert-butyl-3-ethylcyclohexane.

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.