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Videos de Conceptos Relacionados

α-Alkylation of Ketones via Enolate Ions01:10

α-Alkylation of Ketones via Enolate Ions

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Ketones with α protons are deprotonated by strong bases like lithium diisopropylamide (LDA) to form enolate ions. The anion is stabilized by resonance, and its hybrid structure exhibits negative charges on the carbonyl oxygen and the α carbon. This ambident nucleophile can attack an electrophile via two possible sites: the carbonyl oxygen, known as O-attack, or the α carbon, known as C-attack. The nucleophilic attack via the carbanionic site is preferred. This is due to the...
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Regioselective Formation of Enolates01:33

Regioselective Formation of Enolates

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As depicted in the figure below, the unsymmetrical ketones can form two possible enolates:  less substituted or more substituted enolates. Usually, the thermodynamic enolates are formed from the more substituted α-carbon atom, while the kinetic enolates are formed faster by deprotonation from the less substituted position. The thermodynamic enolates have lower energy, so they are  more stable. But the energy required to form kinetic enolates is less.
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Reactivity of Enolate Ions01:23

Reactivity of Enolate Ions

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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, leading to a resonance-stabilized enolate ion where one of the contributing structures is an oxyanion, which imparts additional stability. Therefore, the proton on the α carbon is more acidic in nature than that of other sp3-hybridized C–H bonds but less acidic than those in O–H bonds where the negative charge in the conjugate...
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Aldehydes and Ketones with Amines: Enamine Formation Mechanism01:14

Aldehydes and Ketones with Amines: Enamine Formation Mechanism

8.9K
Enamine formation involves the addition of carbonyl compounds to a secondary amine through a series of reactions. The mechanism begins with the generation of carbinolamine, a nucleophilic attack followed by several proton transfer reactions. The hydroxyl group of the carbinolamine is converted into water to make a better leaving group that can push the reaction forward by eliminating a water molecule. In enamine formation, the last step involves the abstraction of a proton from the α carbon to...
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Types of Enols and Enolates01:19

Types of Enols and Enolates

3.9K
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 undetectable for acetaldehyde, present as only 1.5 × 10−4 % of acetone, and present as only 1.2% of cyclohexanone. Two kinds of regioisomeric enols are possible for unsymmetrical ketones, and their net composition is 1% at equilibrium. This instability is due to the lower bond energy of C=C than the C=O group. The additional...
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Aldehydes and Ketones with Amines: Imine and Enamine Formation Overview01:16

Aldehydes and Ketones with Amines: Imine and Enamine Formation Overview

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Primary amines react with carbonyl compounds—aldehydes and ketones—to generate imines. Imines consist of a C=N double bond and are named Schiff bases after its discoverer—the German chemist Hugo Schiff. On the other hand, secondary amines react with carbonyl compounds to give enamines. In enamines, the presence of a C=C double bond adjacent to the nitrogen atom leads to the delocalization of the lone pair.
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A Protocol for Safe Lithiation Reactions Using Organolithium Reagents
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Estructuras en estado sólido y en solución de enolados de litio derivados de glicinimina

Kyoung Joo Jin1, David B Collum1

  • 1Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University , Ithaca, New York 14853-1301, United States.

Journal of the American Chemical Society
|November 12, 2015
PubMed
Resumen

Este estudio revela las complejas estructuras de agregación de enolados de litio en solución, utilizando técnicas como la cristalografía de rayos X y la espectroscopia de RMN. Los hallazgos detallan las formaciones monómero, dímero, tetrámero y hexámero influenciadas por los aditivos de diamina solvente y quiral.

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Área de la Ciencia:

  • Química organometálica
  • Química supramolecular
  • Síntesis orgánica

Sus antecedentes:

  • Los enolados de litio son intermediarios cruciales en la síntesis orgánica.
  • Comprender su estado de agregación es clave para controlar la reactividad.
  • Las diaminas quirales se utilizan a menudo como aditivos para influir en la estereoquímica.

Objetivo del estudio:

  • Elucidar las estructuras de agregación de los enolados de litio derivados de las gliciniminas.
  • Investigar la influencia de los aditivos solventes y quirales en estas estructuras.
  • Para correlacionar el comportamiento de la solución con las estructuras de estado sólido.

Principales métodos:

  • Cristalografía de rayos X para la determinación de la estructura en estado sólido.
  • (6) Espectroscopia de RMN Li y método de variaciones continuas para estudios de soluciones.
  • Computaciones de la teoría funcional de la densidad (DFT) para conocimientos teóricos.

Principales resultados:

  • Las estructuras cristalinas observadas incluyen monómeros, dímeros, tetrámeros y hexámeros.
  • Los estudios de RMN revelaron la distribución de estas especies en solución.
  • Los cálculos de DFT proporcionaron información detallada sobre las obligaciones y la energía.

Conclusiones:

  • La agregación del enolato de litio depende en gran medida del disolvente y de los aditivos.
  • Las diaminas quirales como TMCDA juegan un papel importante en la formación de la estructura.
  • Una combinación de métodos experimentales y computacionales proporciona una comprensión completa.