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

A-Values

Organic Chemistry

4. Alkanes and Cycloalkanes

A-Values

Previous problemNext problem

5:28 minutes

Problem 20b

Textbook Question

Why is the percentage of molecules with the substituent in an equatorial position greater for isopropylcyclohexane than for fluorocyclohexane?

Verified step by step guidance

Understand the concept of axial and equatorial positions in cyclohexane: Cyclohexane adopts a chair conformation where substituents can occupy either axial (parallel to the ring's axis) or equatorial (pointing outward from the ring) positions. Substituents in the equatorial position experience less steric hindrance compared to axial positions.

Consider the size of the substituent: Isopropyl is a bulky group, while fluorine is relatively small. Larger substituents, like isopropyl, experience significant steric interactions when placed in the axial position due to crowding with axial hydrogens on the same side of the ring.

Analyze the steric hindrance: For isopropylcyclohexane, the steric hindrance caused by the axial position is much greater than for fluorocyclohexane because the isopropyl group is bulkier. This makes the equatorial position more favorable for isopropylcyclohexane to minimize steric strain.

Consider electronic effects: Fluorine is an electronegative atom, and its small size means that steric hindrance is less pronounced. While fluorine may have some electronic preferences, steric factors dominate in determining the preferred position for substituents in cyclohexane.

Conclude the reasoning: The percentage of molecules with the substituent in the equatorial position is greater for isopropylcyclohexane because the bulky isopropyl group strongly favors the equatorial position to reduce steric hindrance, whereas the smaller fluorine substituent does not experience as much steric strain in 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.

Chair Conformation

Cyclohexane can adopt a chair conformation that minimizes steric strain. In this conformation, substituents can occupy either axial or equatorial positions. Equatorial positions are generally more stable because they reduce steric hindrance with other axial substituents, making it crucial to understand how substituents affect stability.

Steric Hindrance

Steric hindrance refers to the repulsion between atoms that occurs when they are brought close together. In cyclohexane derivatives, bulky substituents prefer equatorial positions to minimize interactions with other axial substituents. The degree of steric hindrance varies with the size and shape of the substituents, influencing their preferred positions.

Substituent Effects

Different substituents have varying effects on the stability of cyclohexane conformations. For example, isopropyl groups are larger and create more steric strain when in axial positions compared to smaller groups like fluorine. Understanding these effects helps explain why isopropylcyclohexane has a higher percentage of equatorial substituents compared to fluorocyclohexane.

Watch next

Master Calculating Chair Equilibrium with a bite sized video explanation from Johnny

Start learning

Related Videos

Related Practice

Textbook Question

The A value of a substituent on a cyclohexane ring is essentially the ∆G° for a substituent going from the equatorial to the axial position in a chair–chair interconversion. Because most substituents prefer to be in the equatorial position, A values are, by definition, positive numbers. Use the table of A values to calculate ∆G° and K_eq for the chair–chair interconversions shown.

(b)

Textbook Question

(c)

Textbook Question

(d)

Textbook Question

The ∆G° for conversion of “axial” fluorocyclohexane to “equatorial” fluorocyclohexane at 25 °C is -0.25kcal/mol. Calculate the percentage of fluorocyclohexane molecules that have the fluoro substituent in an equatorial position at equilibrium.

Textbook Question

(a)

Textbook Question

Using the data in Table 3.9, calculate the percentage of molecules of cyclohexanol that have the OH group in an equatorial position at 25 °C.

Textbook Question

Rank the following compounds in order of their total heat of combustion. These compounds are constitutional isomers, each with a molecular formula of C₆H₁₂.

Textbook Question

Which constitutional isomer, A or B, would you expect to have the highest heat of combustion (∆H_combustion)?

Show more practices

Download the Mobile app

Privacy

Do not sell my personal information

Accessibility

Patent notice

Sitemap