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

25. Condensation Chemistry

Conjugate Addition

Organic Chemistry

25. Condensation Chemistry

Conjugate Addition

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3:08 minutes

Problem 55b

Textbook Question

Propose a mechanism for the conjugate addition of a nucleophile (Nuc:^–) to acrylonitrile (H₂C=CHCN) and to nitroethylene. Use resonance forms to show how the cyano and nitro groups activate the double bond toward conjugate addition.

Verified step by step guidance

Identify the structure of acrylonitrile (H₂C=CHCN) and nitroethylene (H₂C=CHNO₂). Both molecules contain an electron-withdrawing group (cyano or nitro) attached to a carbon-carbon double bond, which makes the β-carbon electrophilic and susceptible to nucleophilic attack.

Explain the resonance stabilization of the electron-withdrawing groups. For acrylonitrile, the cyano group (-CN) can delocalize the negative charge through resonance:

H C_{2} = C_{1} C N \leftrightarrow C_{2} - C_{1} = C N

. For nitroethylene, the nitro group (-NO₂) can delocalize the negative charge through resonance:

H C_{2} = C_{1} N O O \leftrightarrow C_{2} - C_{1} = N O O

Describe the nucleophilic attack. The nucleophile (Nuc:-) attacks the β-carbon of the double bond (C2) because it is electrophilic due to the electron-withdrawing effects of the cyano or nitro group. This forms a new bond between the nucleophile and the β-carbon, while the π-bond electrons shift to the α-carbon (C1), creating a carbanion intermediate.

Show the resonance stabilization of the carbanion intermediate. For acrylonitrile, the negative charge on the α-carbon can delocalize into the cyano group:

C_{1} - C_{2} C N \leftrightarrow C_{1} = C_{2} - C N

. For nitroethylene, the negative charge on the α-carbon can delocalize into the nitro group:

C_{1} - C_{2} N O O \leftrightarrow C_{1} = C_{2} - N O O

Conclude the mechanism by protonating the carbanion intermediate. The carbanion formed after the nucleophilic attack is protonated by a suitable proton donor (e.g., water or an acid), resulting in the final product of the conjugate addition reaction. This step restores the stability of the molecule and completes the reaction.

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Key Concepts

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

Conjugate Addition

Conjugate addition refers to the nucleophilic attack on the β-carbon of an α,β-unsaturated carbonyl compound, leading to the formation of a new bond. This reaction typically occurs when a nucleophile adds to the double bond, resulting in a product that retains the original carbonyl functionality. Understanding this mechanism is crucial for analyzing how nucleophiles interact with compounds like acrylonitrile and nitroethylene.

Resonance Stabilization

Resonance stabilization involves the delocalization of electrons across multiple structures, which can enhance the reactivity of a molecule. In the context of acrylonitrile and nitroethylene, the cyano and nitro groups can stabilize the negative charge that develops during nucleophilic attack through resonance, making the double bond more electrophilic. This concept is essential for understanding how these groups activate the double bond toward conjugate addition.

Electrophilicity of Double Bonds

Electrophilicity refers to the tendency of a species to attract electrons, making it susceptible to nucleophilic attack. In α,β-unsaturated systems like acrylonitrile and nitroethylene, the presence of electron-withdrawing groups (EWGs) such as cyano and nitro increases the electrophilicity of the double bond. This enhanced reactivity is a key factor in facilitating the conjugate addition mechanism, as it lowers the energy barrier for the nucleophile to attack.

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Propose a mechanism for the conjugate addition of a nucleophile (Nuc:–) to acrylonitrile (H2C=CHCN) and to nitroethylene. Use resonance forms to show how the cyano and nitro groups activate the double bond toward conjugate addition.

Key Concepts

Conjugate Addition

Resonance Stabilization

Electrophilicity of Double Bonds

Watch next

Propose a mechanism for the conjugate addition of a nucleophile (Nuc:^–) to acrylonitrile (H₂C=CHCN) and to nitroethylene. Use resonance forms to show how the cyano and nitro groups activate the double bond toward conjugate addition.