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

Ring Strain

Organic Chemistry

4. Alkanes and Cycloalkanes

Ring Strain

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4:29 minutes

Problem 50c

Textbook Question

Cyclopropane (C₃H₆, a three-membered ring) is more reactive than most other cycloalkanes.
c. Suggest why cyclopropane is so reactive.

Verified step by step guidance

Cyclopropane is a three-membered ring, which means it has significant angle strain. The ideal bond angle for sp3 hybridized carbon atoms is 109.5 degrees, but in cyclopropane, the bond angles are approximately 60 degrees.

The deviation from the ideal bond angle creates angle strain, which increases the potential energy of the molecule, making it less stable and more reactive.

In addition to angle strain, cyclopropane also experiences torsional strain due to the eclipsing interactions of the hydrogen atoms attached to the carbon atoms in the ring.

The combination of angle strain and torsional strain makes cyclopropane more reactive as the molecule seeks to relieve this strain by undergoing chemical reactions.

Cyclopropane can participate in reactions such as ring-opening reactions, where the strain is relieved by breaking one of the carbon-carbon bonds, leading to more stable, open-chain structures.

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Key Concepts

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

Ring Strain

Cyclopropane experiences significant ring strain due to its three-membered ring structure. The bond angles in cyclopropane are approximately 60 degrees, much smaller than the ideal tetrahedral angle of 109.5 degrees, causing increased angle strain. This strain makes the molecule less stable and more reactive as it seeks to relieve the strain.

Bonding in Cycloalkanes

In cycloalkanes, the carbon atoms are typically sp3 hybridized, forming sigma bonds. However, in cyclopropane, the overlap of orbitals is less effective due to the ring's small size, leading to weaker bonds. This weaker bonding contributes to the molecule's higher reactivity compared to larger, more stable cycloalkanes.

Torsional Strain

Cyclopropane also experiences torsional strain due to the eclipsing of hydrogen atoms attached to the carbon atoms. This eclipsing increases the energy of the molecule, making it more reactive. The combination of torsional and angle strain in cyclopropane results in a highly strained and reactive structure.

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Related Practice

Textbook Question

Which conformation in each of the following pairs has the least strain energy?

(a)

Textbook Question

Choose the conformation in each pair that is most stable. If both are equally stable, then write 'no difference.'

(a)

Textbook Question

The normal C(sp³)–C(sp³) bond length is 1.54 Å. The normal bond angle for an sp³-hybridized carbon is 109.5°. The following molecule experiences large deviations from these normal values. Explain these deviations. [Molecular models would be helpful here.]

Multiple Choice

Which of the following Newman projections has the highest strain energy?

Textbook Question

The heat of combustion of cis-1,2-dimethylcyclopropane is larger than that of the trans isomer. Which isomer is more stable? Use drawings to explain this difference in stability

Textbook Question

Verify the strain energy shown in Table 3.8 for cycloheptane

Textbook Question

The heat of combustion of cis-1,2-dimethylcyclopropane is larger than that of the trans isomer. Which isomer is more stable? Use drawings to explain this difference in stability.

Textbook Question

Which conformation in each of the following pairs has the least strain energy?

(b)

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