Kapitel 15
α-Kohlenstoffchemie: Enole, Enolate und Enamine
Reaktivität von Enolen
Enols are a class of compounds where a hydroxyl group is attached to a carbon–carbon double bond, which implies that it is a vinyl alcohol. A ...
Reaktivität von Enolat Ionen
Enolate ions are formed by the acid–base reaction of a carbonyl compound with a base. This leads to deprotonation of the α hydrogen atom, ...
Arten von Enolen und Enolaten
Aldehydes and ketones form enols, although only about 1% of the enol is present at the equilibrium for simple monocarbonyl compounds. The enol form is ...
Konventionen des Enolat Mechanismus
When a carbonyl compound is treated with a strong base, the α position gets deprotonated to give a resonance-stabilized intermediate called an ...
Regioselektive Bildung von Enolaten
As depicted in the figure below, the unsymmetrical ketones can form two possible enolates: less substituted or more substituted enolates. Usually, ...
Stereochemische Effekte der Enolisierung
The chiral α-carbon of the carbonyl compound is the stereocenter of the molecule. As shown in the figure below, when such a carbonyl compound ...
Säurekatalysierte α-Halogenierung von Aldehyden und Ketonen
By replacing an α-hydrogen with a halogen, acid-catalyzed α-halogenation of aldehydes or ketones yields a monohalogenated product
In the first ...
Basenkatalysierte α-Halogenierung von Aldehyden und Ketonen
α-Halogenation of aldehydes and ketones is a reaction involving the substitution of α hydrogens with halogens in the presence of a base. ...
Mehrfache Halogenierung von Methylketonen: Haloform-Reaktion
A method involving the transformation of methyl ketones to carboxylic acids using excess base and halogen is called the haloform reaction. It begins with ...
α-Halogenierung von Carbonsäurederivaten: Überblick
Unlike aldehydes and ketones, carboxylic acids do not readily participate in α halogenation reactions via enols or enolate intermediates. However, ...
α-Bromierung von Carbonsäuren: Hell-Volhard-Zelinsky-Reaktion
The method to achieve α-brominated carboxylic acids using a mixture of phosphorus tribromide and bromine is known as the ...
Reaktionen von α-Halocarbonyl-Verbindungen: Nukleophile Substitution
Nucleophilic substitution in α-halocarbonyl compounds can be achieved via an SN2 pathway. The reaction in α-haloketones is generally carried out ...
Nitrosierung von Enolen
The nitrosation reaction is one of the methods of preparing 1,2-diketones. The enol tautomer of the starting ketone reacts with sodium nitrite in ...
Bildung von C-C-Bindungen: Überblick über die Aldolkondensation
Aldol condensation is an important route in synthetic organic chemistry used to generate a new carbon–carbon bond under basic or acidic conditions. ...
Basenkatalysierte Aldoladditionsreaktion
As depicted in Figure 1, base-catalyzed aldol addition involves adding two carbonyl compounds in aqueous sodium hydroxide to form a β-hydroxy ...
Säurekatalysierte Aldoladditionsreaktion
The aldol reaction of a ketone under acidic conditions successfully forms an unsaturated carbonyl as the final product instead of an aldol. The ...
Dehydratisierung von Aldolen zu Enalen: Basenkatalysierte Aldolkondensation
This lesson delves into the aldol condensation catalyzed by bases, where aldols undergo dehydration to enals. As shown in Figure 1, the β-hydroxy ...
Dehydratisierung von Aldolen zu Enonen: Säurekatalysierte Aldolkondensation
As shown in Figure 1, under acidic conditions, the β-hydroxy ketone undergoes dehydration via an E1 elimination reaction to form an enone.
Figure 1. ...
Intramolekulare Aldolreaktion
Intramolecular aldol reaction occurs in dicarbonyl compounds such as dialdehydes, diketones, and keto-aldehydes. The dicarbonyl compounds possess more ...
C-C-Bindungsspaltung: Retroadolreaktion
The reverse of the aldol addition reaction is called the retro-aldol reaction. Here, the carbon–carbon bond in the aldol product is cleaved under ...
Gekreuzte Aldolreaktionen: Übersicht
Crossed aldol addition is the reaction between two different carbonyl compounds under acidic or basic conditions. Here, both the carbonyl compounds ...
Gekreuzte Aldolreaktion mit schwachen Basen
This lesson deals with the crossed aldol reaction using weak bases. The self-condensation of an aldehyde having α hydrogen is prevented by adding it ...
Ketone mit nicht enolisierbaren aromatischen Aldehyden: Claisen-Schmidt-Kondensation
Benzaldehyde, like formaldehyde, lacks an α hydrogen and cannot enolize to form an enolate. Hence, the reaction of benzaldehyde with a ketone in the ...
Gekreuzte Aldolreaktion mit starken Basen: Gerichtete Aldolreaktion
The reaction between two different carbonyl compounds comprising α hydrogen in the presence of a strong base like lithium diisopropylamide (LDA) to ...
Aldolkondensation mit β-Diestern: Knoevenagel-Kondensation
The Knoevenagel condensation is an aldol-type reaction involving the condensation of aldehydes or ketones with active methylene compounds such as ...
Ester zu β-Ketoestern: Überblick über die Claisen-Kondensation
Regular Claisen condensation is a base-promoted reaction involving identical esters with two α hydrogens, condensing to produce β-ketoesters. It ...
Ester zu β-Ketoestern: Mechanismus der Claisen-Kondensation
Regular Claisen condensation involves the synthesis of β-ketoesters by combining identical ester molecules bearing two α hydrogens in the ...
Aldolkondensation vs. Claisen-Kondensation
Aldol condensation is an acid or base-catalyzed condensation between aldehydes or ketones to give an α,ꞵ-unsaturated carbonyl compound. A ...
Intramolekulare Claisen-Kondensation von Dicarboxyl-Estern: Dieckmann-Cyclisierung
Dieckmann cyclization is an intramolecular Claisen condensation of diesters. The reaction occurs in the presence of a base and generates a cyclic ...
β-Dicarbonyl-Verbindungen über gekreuzte Claisen-Kondensationen
Crossed Claisen condensations are base-promoted reactions between two different ester molecules producing β-dicarbonyl compounds. The reaction ...
α-Alkylierung von Ketonen über Enolat-Ionen
Ketones with α protons are deprotonated by strong bases like lithium diisopropylamide (LDA) to form enolate ions. The anion is stabilized by ...
Faktoren, die die α-Alkylierung von Ketonen beeinflussen: Wahl der Base
α-Alkylation of ketones is achieved in the presence of alkyl halides and a base. The reaction proceeds via the formation of an enolate ion followed ...
Alkylierung von β-Ketoester-Enolaten: Acetessigester-Synthese
Acetoacetic ester synthesis is a method to obtain ketones from alkyl halides and β-keto esters. The reaction occurs in the presence of an alkoxide ...
Alkylierung von β-Diester-Enolaten: Malonester-Synthese
Malonic ester synthesis is a method to obtain α substituted carboxylic acids from ꞵ-diesters such as diethyl malonate and alkyl halides.
The ...
Konjugierte Addition an α,β-ungesättigte Carbonyl-Verbindungen
α,β-Unsaturated carbonyl compounds are molecules bearing a carbonyl and alkene functionality in conjugation with each other. The conjugation in ...
Konjugierte Addition (1,4-Addition) vs. direkte Addition (1,2-Addition)
α,β-Unsaturated carbonyl compounds with two electrophilic sites, the carbonyl carbon, and the β carbon, are susceptible to nucleophilic ...
Konjugierte Addition von Enolaten: Michael-Addition
The attack of a nucleophile at the β carbon of an α,β-unsaturated carbonyl compound is called conjugate addition. Conjugate addition ...
Cyclohexenone über Michael-Addition und Aldol-Kondensation: Die Robinson-Anellierung
Robinson annulation is a base-catalyzed reaction for the synthesis of 2-cyclohexenone derivatives from 1,3-dicarbonyl donors (such as cyclic diketones, ...
Synthese von α-substituierten Carbonyl-Verbindungen: Die Stork-Enamin-Reaktion
α-Substituted ketones or aldehydes can be synthesized from enamines by the Stork enamine reaction, named after its pioneer Gilbert Stork. Enamines ...
Nicht enolisierbare Aldehyde zu Säuren und Alkoholen: Die Cannizzaro-Reaktion
The Cannizzaro reaction is a base-promoted redox reaction producing a primary alcohol and a carboxylic acid from two molecules of a nonenolizable ...
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