Capítulo 15
Química do Carbono α: Enóis, Enolatos e Enaminas
Reatividade de Enóis
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 ...
Reatividade de Íons Enolato
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, ...
Tipos de Enóis e Enolatos
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 ...
Convenções do Mecanismo do Enolato
When a carbonyl compound is treated with a strong base, the α position gets deprotonated to give a resonance-stabilized intermediate called an ...
Formação Regiosseletiva de Enolatos
As depicted in the figure below, the unsymmetrical ketones can form two possible enolates: less substituted or more substituted enolates. Usually, ...
Efeitos Estereoquímicos da Enolização
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 ...
α-Halogenação de Aldeídos e Cetonas Catalisada por Ácido
By replacing an α-hydrogen with a halogen, acid-catalyzed α-halogenation of aldehydes or ketones yields a monohalogenated product
In the first ...
α-Halogenação de Aldeídos e Cetonas Promovida por Base
α-Halogenation of aldehydes and ketones is a reaction involving the substitution of α hydrogens with halogens in the presence of a base. ...
Halogenação Múltipla de Metil-Cetonas: Reação de Halofórmio
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-Halogenação de Derivados de Ácido Carboxílico: Visão Geral
Unlike aldehydes and ketones, carboxylic acids do not readily participate in α halogenation reactions via enols or enolate intermediates. However, ...
α-Bromação de Ácidos Carboxílicos: Reação Hell-Volhard-Zelinski
The method to achieve α-brominated carboxylic acids using a mixture of phosphorus tribromide and bromine is known as the ...
Reações de Compostos α-Halocarbonílicos: Substituição Nucleofílica
Nucleophilic substitution in α-halocarbonyl compounds can be achieved via an SN2 pathway. The reaction in α-haloketones is generally carried out ...
Nitrosação de Enóis
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 ...
Formação da Ligação C-C: Visão Geral da Condensação Aldólica
Aldol condensation is an important route in synthetic organic chemistry used to generate a new carbon–carbon bond under basic or acidic conditions. ...
Reação de Adição Aldólica Catalisada por Base
As depicted in Figure 1, base-catalyzed aldol addition involves adding two carbonyl compounds in aqueous sodium hydroxide to form a β-hydroxy ...
Reação de Adição Aldólica Catalisada por Ácido
The aldol reaction of a ketone under acidic conditions successfully forms an unsaturated carbonyl as the final product instead of an aldol. The ...
Desidratação Aldólica para Enals: Condensação Aldólica Catalisada por Base
This lesson delves into the aldol condensation catalyzed by bases, where aldols undergo dehydration to enals. As shown in Figure 1, the β-hydroxy ...
Desidratação de Aldóis para Enonas: Condensação Aldólica Catalisada por Ácido
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. ...
Reação Aldólica Intramolecular
Intramolecular aldol reaction occurs in dicarbonyl compounds such as dialdehydes, diketones, and keto-aldehydes. The dicarbonyl compounds possess more ...
Clivagem da Ligação C-C: Reação Retro-Aldólica
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 ...
Reações Aldólicas Cruzadas: Visão Geral
Crossed aldol addition is the reaction between two different carbonyl compounds under acidic or basic conditions. Here, both the carbonyl compounds ...
Reação Aldólica Cruzada Usando Bases Fracas
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 ...
Cetonas com Aldeídos Aromáticos Não Enolizáveis: Condensação de Claisen-Schmidt
Benzaldehyde, like formaldehyde, lacks an α hydrogen and cannot enolize to form an enolate. Hence, the reaction of benzaldehyde with a ketone in the ...
Reação Aldólica Cruzada Usando Bases Fortes: Reação Aldólica Direcionada
The reaction between two different carbonyl compounds comprising α hydrogen in the presence of a strong base like lithium diisopropylamide (LDA) to ...
Condensação Aldólica com β-Diésteres: Condensação de Knoevenagel
The Knoevenagel condensation is an aldol-type reaction involving the condensation of aldehydes or ketones with active methylene compounds such as ...
Ésteres para β-Cetoésteres: Visão Geral da Condensação de Claisen
Regular Claisen condensation is a base-promoted reaction involving identical esters with two α hydrogens, condensing to produce β-ketoesters. It ...
Ésteres a β-Cetoésteres: Mecanismo de Condensação de Claisen
Regular Claisen condensation involves the synthesis of β-ketoesters by combining identical ester molecules bearing two α hydrogens in the ...
Condensação Aldólica vs Condensação de Claisen
Aldol condensation is an acid or base-catalyzed condensation between aldehydes or ketones to give an α,ꞵ-unsaturated carbonyl compound. A ...
Condensação de Claisen Intramolecular de Ésteres Dicarboxílicos: Ciclização de Dieckmann
Dieckmann cyclization is an intramolecular Claisen condensation of diesters. The reaction occurs in the presence of a base and generates a cyclic ...
Compostos β-Dicarbonílicos via Condensações cruzadas de Claisen
Crossed Claisen condensations are base-promoted reactions between two different ester molecules producing β-dicarbonyl compounds. The reaction ...
α-Alquilação de Cetonas via Íons Enolato
Ketones with α protons are deprotonated by strong bases like lithium diisopropylamide (LDA) to form enolate ions. The anion is stabilized by ...
Fatores que Afetam a α-Alquilação de Cetonas: Escolha da 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 ...
Alquilação de Enolatos de β-Cetoéster: Síntese de Éster Acetoacético
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 ...
Alquilação de Enolatos de β-Diéster: Síntese de Éster Malônico
Malonic ester synthesis is a method to obtain α substituted carboxylic acids from ꞵ-diesters such as diethyl malonate and alkyl halides.
The ...
Adição de conjugado a compostos carbonílicos α,β-insaturados
α,β-Unsaturated carbonyl compounds are molecules bearing a carbonyl and alkene functionality in conjugation with each other. The conjugation in ...
Adição Conjugada (1,4-Adição) vs Adição Direta (1,2-Adição)
α,β-Unsaturated carbonyl compounds with two electrophilic sites, the carbonyl carbon, and the β carbon, are susceptible to nucleophilic ...
Adição Conjugada de Enolatos: Adição de Michael
The attack of a nucleophile at the β carbon of an α,β-unsaturated carbonyl compound is called conjugate addition. Conjugate addition ...
Ciclohexenonas via Adição de Michael e condensação Aldólica: Anulação de Robinson
Robinson annulation is a base-catalyzed reaction for the synthesis of 2-cyclohexenone derivatives from 1,3-dicarbonyl donors (such as cyclic diketones, ...
Síntese de Compostos Carbonílicos α-Substituídos: A Reação de Enamina de Stork
α-Substituted ketones or aldehydes can be synthesized from enamines by the Stork enamine reaction, named after its pioneer Gilbert Stork. Enamines ...
Aldeídos Não-Enolizáveis a Ácidos e Álcoois: Reação de Cannizzaro
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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