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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2:17 minutes

Problem 86

Textbook Question

Bromine is a larger atom than chlorine, but the equilibrium constants in Table 3.9 indicate that a chloro substituent has a greater preference for the equatorial position than does a bromo substituent. Suggest an explanation for this fact.

Verified step by step guidance

Understand the context: The problem involves the preference of substituents (chloro and bromo) for the equatorial position in a cyclohexane chair conformation. This preference is influenced by steric and electronic factors.

Recall the steric hindrance concept: Bromine (Br) is a larger atom than chlorine (Cl), so you might initially expect bromine to have a stronger preference for the equatorial position to minimize steric interactions with axial hydrogens.

Consider electronic effects: Chlorine is more electronegative than bromine, which means it can withdraw electron density more effectively. This can influence the stability of the molecule in different conformations.

Analyze dipole-dipole interactions: The axial position of a substituent can lead to unfavorable dipole-dipole interactions with other axial groups. Chlorine's higher electronegativity may amplify these unfavorable interactions when in the axial position, making the equatorial position more favorable for chlorine.

Conclude the reasoning: The greater preference of chlorine for the equatorial position compared to bromine is likely due to a combination of steric and electronic effects, with chlorine's higher electronegativity playing a significant role in stabilizing the equatorial conformation.

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Key Concepts

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

Sterics and Steric Hindrance

Sterics refers to the spatial arrangement of atoms in a molecule and how this affects molecular interactions. Steric hindrance occurs when larger groups, like bromine, create more crowding around a central atom, making it less favorable for those groups to occupy certain positions, such as the equatorial position in cyclohexane rings.

Equatorial vs. Axial Positions

In cyclohexane, substituents can occupy equatorial or axial positions. Equatorial positions are generally more stable because they minimize steric interactions with other axial substituents. Chlorine, being smaller than bromine, can fit more comfortably in the equatorial position, leading to a greater preference for this arrangement compared to bromine.

Substituent Size and Electronic Effects

The size of a substituent affects its electronic interactions with the rest of the molecule. Chlorine, while larger than hydrogen, is smaller than bromine and has a stronger inductive effect, which can stabilize the equatorial position. This electronic effect, combined with steric factors, explains why chloro substituents prefer equatorial positions more than bromo substituents.

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Related Practice

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.

a. cis-1-ethyl-2-isopropylcyclohexane

b. trans-1-ethyl-2-isopropylcyclohexane

Textbook Question

Draw the two chair conformations of each of the following substituted cyclohexanes. In each case, label the more stable conformation.]

c. cis-1-ethyl-4-isopropylcyclohexane

d. trans-1-ethyl-4-methylcyclohexane

Textbook Question

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

f. cis-1-ethyl-4-isopropylcyclohexane

Textbook Question

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

c. trans-1-ethyl-2-isopropylcyclohexane

Textbook Question

Draw the most stable conformer of the following molecule. (A solid wedge points out of the plane of the paper toward the viewer. A hatched wedge points back from the plane of the paper away from the viewer.)

Textbook Question

Which has a higher percentage of the diequatorial-substituted conformer compared with the diaxialsubstituted conformer: trans-1,4-dimethylcyclohexane or cis-1-tert-butyl-3-methylcyclohexane?

Textbook Question

The most stable form of glucose (blood sugar) is a six-membered ring in a chair conformation with its five substituents all in equatorial positions. Draw the most stable conformer of glucose by putting the OH groups and hydrogens on the appropriate bonds in the structure on the right.

Textbook Question

Draw two chair conformations of the molecules below. Indicate which is most stable.

(a)

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