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

9. Alkenes and Alkynes

Alkene Stability

Organic Chemistry

9. Alkenes and Alkynes

Alkene Stability

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3:48 minutes

Problem 14h,i

Textbook Question

Explain why each of the following alkenes is stable or unstable.
(h)
(i)

Verified step by step guidance

Step 1: Analyze the first alkene structure (image h). The double bond is part of a large ring system. Consider the ring strain and steric hindrance in the molecule. Larger rings generally have less ring strain compared to smaller rings, making the alkene more stable.

Step 2: Evaluate the second alkene structure (image i). The double bond is part of a bicyclic system. Bicyclic systems often have significant ring strain due to the rigid structure and limited flexibility, which can destabilize the alkene.

Step 3: Consider the hybridization of the carbon atoms involved in the double bond for both structures. Sp2 hybridized carbons in alkenes are planar, and any deviation from planarity due to ring strain can affect stability.

Step 4: Assess the substituents around the double bond in both structures. Substituents can stabilize alkenes through hyperconjugation or inductive effects. For example, alkyl groups attached to the double bond can donate electron density, stabilizing the alkene.

Step 5: Compare the overall molecular geometry and steric interactions in both structures. The first structure (h) likely has less steric hindrance and strain compared to the second structure (i), making it more stable. The second structure (i) has a rigid bicyclic framework, which increases strain and reduces stability.

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Key Concepts

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

Alkene Stability

The stability of alkenes is influenced by the degree of substitution around the double bond. More substituted alkenes, such as tetrasubstituted ones, are generally more stable due to hyperconjugation and the electron-donating effects of alkyl groups, which help to stabilize the double bond.

Geometric Isomerism

Alkenes can exhibit geometric isomerism (cis/trans or E/Z isomerism) due to the restricted rotation around the double bond. The spatial arrangement of substituents affects the steric interactions and overall stability of the molecule, with trans isomers typically being more stable than their cis counterparts due to reduced steric strain.

Resonance and Conjugation

Resonance and conjugation can significantly enhance the stability of alkenes. When alkenes are part of a conjugated system, the delocalization of electrons across multiple bonds can lower the overall energy of the molecule, making it more stable compared to isolated double bonds.

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Related Practice

Textbook Question

Of the compounds you named in Problem 45:

a. Which is the most stable?

Textbook Question

Of the compounds you named in Problem 45:

b. Which is the least stable?

Textbook Question

Which species in each pair is more stable?

Textbook Question

Use the data in Table 7-2 to predict the energy difference between 2,3-dimethylbut-1-ene and 2,3-dimethylbut-2-ene. Which of these double-bond isomers is more stable?

Textbook Question

For each set of isomers, choose the isomer that you expect to be most stable and the isomer you expect to be least stable.

(b)

Textbook Question

For each set of isomers, choose the isomer that you expect to be most stable and the isomer you expect to be least stable.

(c)

Textbook Question

In 1935, J. Bredt, a German chemist, proposed that a bicycloalkene could not have a double bond at a bridgehead carbon unless one of the rings contains at least eight carbons. This is known as Bredt's rule. Explain why there cannot be a double bond at this position.

Textbook Question

Rank the following compounds from most stable to least stable:

trans-3-hexene, cis-3-hexene, cis-2,5-dimethyl-3-hexene, (Z)-3,4-dimethyl-3-hexene

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