We show in Chapter 20 that α , β-unsaturated ketones are electrophilic at C 4 . Rationalize this observation.

Hello, everyone. Today, we've got the following problem. Refer to the structure of E he PS three E 20 and alpha beta unsaturated ketone. The compound is electrolytic at carbon two and carbon four. Explain why this is so and then we have answer choices A through D with a saying that they're electrolytic due to the separation of charges that arise from residents when these carbons acquire a positive charge. B saying that they, that contrary to that claim that they're electrolytic, they're highly nuclear affiliate due to triple bonds with C saying that they're electrophysics because they have even numbered carbons or they aren't even number carbons and D saying that it's electrophysics two carbons because they're both S P hybridized. So let's go to these answer choices and start first with the re structure. So actually, we do have a resonant structure that we can create where we take one of these pi electrons from this carbon double bond and move it on to that oxygen such that we create the following resonant structure that has a negative charge on the oxygen and a positive charge on carbon two. We also have analytic pi bond. So we can actually construct another resonant structure where in that carbo call is not on carbon two anymore, but on carbon four. And so we can conclude that answer choice A is actually the correct answer. We can see why B is incorrect because the there are no triple bonds with carbons two and four C is incorrect because even number carbons has no correlation with electro Felicity and D is incorrect because carbons two and four are not S P hybridized. They are S P two hybridized because they're bonded to three different electro domains. And so with that, we've answered the question overall, I hope this helped. And until next time.

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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

3. Acids and Bases

Reaction Mechanism

Organic Chemistry

3. Acids and Bases

Reaction Mechanism

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1:43 minutes

Problem 79

Textbook Question

We show in Chapter 20 that α , β-unsaturated ketones are electrophilic at C₄. Rationalize this observation.

Verified step by step guidance

Understand the structure of α, β-unsaturated ketones: These compounds contain a conjugated system where a carbonyl group (C=O) is directly connected to a double bond (C=C). This conjugation allows for delocalization of electrons across the π-system, which is key to their reactivity.

Analyze the electrophilicity of the β-carbon (C₄): The conjugated system creates resonance structures. One important resonance structure shows the movement of electrons from the double bond toward the oxygen atom of the carbonyl group, resulting in a partial positive charge on the β-carbon (C₄). This makes C₄ electrophilic and susceptible to nucleophilic attack.

Write the resonance structures: To rationalize the observation, draw the resonance structures of the α, β-unsaturated ketone. Show how the electrons from the π-bond of the C=C double bond shift toward the carbonyl oxygen, creating a positive charge on C₄. Use MathML to represent the resonance structures clearly.

Consider the role of the carbonyl group: The carbonyl oxygen is highly electronegative and pulls electron density away from the conjugated system. This effect further enhances the partial positive charge on C₄, increasing its electrophilicity.

Relate this to reactivity: The electrophilic nature of C₄ explains why α, β-unsaturated ketones are reactive at this position. Nucleophiles are attracted to the positively charged C₄, leading to addition reactions at this site. This concept will be explored in more detail in Chapter 20.

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Key Concepts

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

Electrophilicity

Electrophilicity refers to the tendency of a species to accept electrons. In organic chemistry, electrophiles are typically electron-deficient species that can react with nucleophiles, which are electron-rich. Understanding the factors that influence electrophilicity, such as the presence of electron-withdrawing groups, is crucial for rationalizing the reactivity of compounds like α, β-unsaturated ketones.

α, β-Unsaturated Ketones

α, β-Unsaturated ketones are compounds that contain a carbonyl group (C=O) adjacent to a double bond (C=C). This structural feature creates a conjugated system that stabilizes the molecule and enhances its electrophilic character at the β-carbon. The resonance between the carbonyl and the double bond plays a significant role in determining the reactivity of these compounds.

Resonance Stabilization

Resonance stabilization occurs when a molecule can be represented by multiple valid Lewis structures, leading to a delocalization of electrons. In α, β-unsaturated ketones, the resonance between the carbonyl and the adjacent double bond increases the positive character at the β-carbon, making it more electrophilic. This concept is essential for understanding why these compounds are reactive towards nucleophiles.

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