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Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711당신이 사용하는 게 아니라요?교과서 변경
모든 교과서Bruice 8th EditionCh. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions문제 7
22장, 문제 7

Although metal ions increase the rate of decarboxylation of dimethyloxaloacetate, they have no effect on the rate of decarboxylation of either the monoethyl ester of dimethyloxaloacetate or acetoacetate. Explain why this is so.
Structures of dimethyloxaloacetate, monoethyl ester of dimethyloxaloacetate, and acetoacetate with labels.

검증된 단계별 안내
1
Understand the role of metal ions in catalysis: Metal ions can stabilize negative charges that develop during a reaction, particularly on intermediates or transition states. This stabilization lowers the activation energy, increasing the reaction rate.
Analyze the structure of dimethyloxaloacetate: Dimethyloxaloacetate contains two ester groups and a β-keto group. During decarboxylation, the β-keto group forms an enolate intermediate, which has a negative charge on the oxygen atom. Metal ions can stabilize this enolate intermediate, facilitating the reaction.
Compare with the monoethyl ester of dimethyloxaloacetate: The monoethyl ester has one ester group replaced with an ethyl group. This structural change reduces the ability of the molecule to form a stabilized enolate intermediate, as the electron-withdrawing effect of the ester group is diminished. Metal ions cannot significantly stabilize the intermediate in this case, so the rate of decarboxylation is unaffected.
Examine acetoacetate: Acetoacetate is a β-keto acid that undergoes decarboxylation to form an enolate intermediate. However, the enolate intermediate in this case is already stabilized by resonance, and the reaction does not require additional stabilization from metal ions. Thus, metal ions have no effect on the rate of decarboxylation.
Conclude the reasoning: The difference in the effect of metal ions on the decarboxylation rates is due to the structural differences in the molecules and the extent to which the enolate intermediate or transition state can be stabilized by metal ions. Dimethyloxaloacetate benefits from metal ion stabilization, while the monoethyl ester and acetoacetate do not.

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5m

주요 개념

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

Decarboxylation

Decarboxylation is a chemical reaction that involves the removal of a carboxyl group (-COOH) from a molecule, resulting in the release of carbon dioxide (CO2). This process is crucial in organic chemistry, particularly in metabolic pathways and the synthesis of various compounds. The rate of decarboxylation can be influenced by factors such as the structure of the substrate and the presence of catalysts, including metal ions.
추천 영상:
02:32
Predict the correct structure

Metal Ion Catalysis

Metal ion catalysis refers to the acceleration of chemical reactions by metal ions, which can stabilize transition states or intermediates. In the context of decarboxylation, metal ions may facilitate the reaction by coordinating with the substrate, thereby lowering the activation energy required for the reaction to proceed. However, the effectiveness of metal ions can vary depending on the specific substrate and its electronic and steric properties.
추천 영상:
가이드 코스
3:39
Metal Ion Catalysis Concept 1

Substrate Structure and Reactivity

The structure of a substrate significantly influences its reactivity in chemical reactions. In the case of dimethyloxaloacetate, the presence of specific functional groups and steric factors may make it more susceptible to decarboxylation in the presence of metal ions. Conversely, the monoethyl ester of dimethyloxaloacetate and acetoacetate may have structural features that render them less reactive or less dependent on metal ion catalysis, explaining the observed differences in reaction rates.
추천 영상:
01:17
Reactivity of Molecules
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Draw the mechanism if it involves general-acid catalysis.

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교과서 질문

a. Draw the mechanism for the following reaction if it involves specific-base catalysis.

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Draw the mechanism for the following reaction if it involves specific-acid catalysis.

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교과서 질문

Show all the products, including their configurations, that are obtained from the above reaction.

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