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Show how the following products might be synthesized from suitable Michael donors and acceptors.
(c)
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Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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TOC.tableOfContents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
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Wade 9th EditionCh. 22 - Condensations and Alpha Substitutions of Carbonyl CompoundsProblema 55b
Wade 9th EditionCh. 22 - Condensations and Alpha Substitutions of Carbonyl CompoundsProblema 55bCapitolo 22, Problema 55b
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.
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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: . For nitroethylene, the nitro group (-NO₂) can delocalize the negative charge through resonance: .
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: . For nitroethylene, the negative charge on the α-carbon can delocalize into the nitro group: .
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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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.
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09:23
1,2 vs 1,4 Addition
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.
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03:43The radical stability trend.
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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06:00Single bonds, double bonds, and triple bonds.
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