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シンジェスティック・ノンコヴァレンント・カタリシス ベースフリー・マイケル・アディション

  • 0EaStCHEM School of Chemistry, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh, Scotland EH9 3FJ, United Kingdom.

まとめ

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Conjugate Addition of Enolates: Michael Addition 01:08

3.1K

The attack of a nucleophile at the β carbon of an α,β-unsaturated carbonyl compound is called conjugate addition. Conjugate addition reactions of active methylene compounds, such as β-diketones, β-keto esters, β-keto nitriles, and α-nitro ketones, are called Michael addition reactions.

The reaction is catalyzed by a base that abstracts the acidic methylene hydrogen, generating a doubly-stabilized enolate ion that serves as the nucleophile or the Michael donor. The base employed depends...

Cycloaddition Reactions: MO Requirements for Thermal Activation 01:16

4.0K

Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.

The reaction occurs between the highest occupied molecular orbital (HOMO) of one π component and the lowest unoccupied molecular orbital (LUMO) of the other. These are known as...

Conjugate Addition (1,4-Addition) vs Direct Addition (1,2-Addition) 01:27

4.0K

α,β-Unsaturated carbonyl compounds with two electrophilic sites, the carbonyl carbon, and the β carbon, are susceptible to nucleophilic attack via two modes: conjugate or 1,4-addition and direct or 1,2-addition.
Conjugate addition results in a thermodynamically stable product. The reaction retains the stronger C=O bond at the expense of the weaker C=C π bond. The process is slow as the β carbon is less electrophilic than the carbonyl carbon.
Direct addition products are...

Radical Anti-Markovnikov Addition to Alkenes: Mechanism 01:17

4.4K

The reaction of hydrogen bromide with alkenes in the presence of hydroperoxides or peroxides proceeds via anti-Markovnikov addition. The radical chain reaction comprises initiation, propagation, and termination steps.
The mechanism starts with chain initiation, which involves two steps. In the first chain initiation step, a weak peroxide bond is homolytically cleaved upon mild heating to form two alkoxy radicals. In the second initiation step, a hydrogen atom is abstracted by the alkoxy...

Nucleophilic Aromatic Substitution: Elimination–Addition 01:11

4.8K

Simple aryl halides do not react with nucleophiles. However, nucleophilic aromatic substitutions can be forced under certain conditions, such as high temperatures or strong bases. The mechanism of substitution under such conditions involves the highly unstable and reactive benzyne intermediate. Benzyne contains equivalent carbon centers at both ends of the triple bond, each of which is equally susceptible to nucleophilic attack. This 50–50 distribution of products is...

Base-Catalyzed Aldol Addition Reaction 01:08

4.2K

As depicted in Figure 1, base-catalyzed aldol addition involves adding two carbonyl compounds in aqueous sodium hydroxide to form a β-hydroxy carbonyl compound.

Figure 1: The base-catalyzed aldol addition reaction of aldehydes.
The reaction preferentially occurs with simple aldehydes, where the α carbon is monosubstituted. The equilibrium of the reaction involving disubstituted aldehydes and ketones shifts backward to the reactants due to the steric interactions at the α carbon. The...