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Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728당신이 사용하는 게 아니라요?교과서 변경
모든 교과서Wade 9th EditionCh. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds문제 55b
22장, 문제 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.

검증된 단계별 안내
1
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: HC2=C1CN↔C2−C1=CN. For nitroethylene, the nitro group (-NO₂) can delocalize the negative charge through resonance: HC2=C1NOO↔C2−C1=NOO.
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: C1−C2CN↔C1=C2−CN. For nitroethylene, the negative charge on the α-carbon can delocalize into the nitro group: C1−C2NOO↔C1=C2−NOO.
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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이 영상 해법은 위 문제에 도움이 된다고 튜터들이 추천한 것입니다.
영상 길이:
3m

주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

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.
추천 영상:
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.
추천 영상:
03:43
The 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.
추천 영상:
06:00
Single bonds, double bonds, and triple bonds.
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