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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2:07 minutes

Problem 15b

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)

Verified step by step guidance

Step 1: Analyze the structures provided. Each structure contains a ketone functional group (C=O) and double bonds in the carbon chain. The stability of these isomers depends on the position of the double bonds relative to the ketone group and the conjugation effects.

Step 2: Consider conjugation. Conjugation occurs when the double bonds are in proximity to the ketone group, allowing for delocalization of electrons. Greater conjugation typically increases stability due to resonance stabilization.

Step 3: Evaluate steric hindrance. Steric hindrance arises when bulky groups or double bonds are positioned close to each other, leading to repulsion and decreased stability. Structures with less steric hindrance are generally more stable.

Step 4: Assess hyperconjugation. Hyperconjugation involves the interaction of sigma bonds with adjacent pi systems, which can stabilize the molecule. Double bonds closer to alkyl groups may benefit from hyperconjugation effects.

Step 5: Rank the isomers based on these factors. The most stable isomer will likely have the greatest conjugation and minimal steric hindrance, while the least stable isomer will have minimal conjugation and significant steric hindrance.

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Key Concepts

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

Isomerism

Isomerism refers to the phenomenon where two or more compounds have the same molecular formula but different structural arrangements or spatial orientations. In organic chemistry, isomers can be classified into structural isomers, which differ in the connectivity of atoms, and stereoisomers, which differ in the spatial arrangement of atoms. Understanding isomerism is crucial for predicting the properties and reactivity of organic compounds.

Stability of Alkenes

The stability of alkenes is influenced by factors such as steric hindrance and the degree of substitution at the double bond. Generally, more substituted alkenes (those with more alkyl groups attached to the carbon atoms of the double bond) are more stable due to hyperconjugation and the inductive effect. Recognizing these stability trends is essential for determining which isomer is likely to be more or less stable in a given set of alkenes.

Trans vs. Cis Isomers

Trans and cis isomers are specific types of stereoisomers that differ in the orientation of substituents around a double bond. In cis isomers, substituents are on the same side of the double bond, while in trans isomers, they are on opposite sides. Generally, trans isomers are more stable than cis isomers due to reduced steric strain, making it important to consider these configurations when evaluating the stability of isomers.

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Related Practice

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

Explain why each of the following alkenes is stable or unstable.

(h)

(i)

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

Textbook Question

The energy difference between cis- and trans-but-2-ene is about 4 kJ/mol; however, the trans isomer of 4,4-dimethylpent-2-ene is nearly 16 kJ/mol more stable than the cis isomer. Explain this large difference.

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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)

Key Concepts

Isomerism

Stability of Alkenes

Trans vs. Cis Isomers

Watch next

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)