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Related Concept Videos

Aromatic Hydrocarbon Anions: Structural Overview01:18

Aromatic Hydrocarbon Anions: Structural Overview

Neutral hydrocarbons like cyclopentadiene with an odd number of carbon atoms and one intervening CH2 group in the ring are not aromatic. Cyclopentadiene with 4 π electrons does not satisfy the 4n + 2 π electron rule. Additionally, the intervening CH2 group is sp3 hybridized and lacks a vacant p orbital, thereby interrupting the overlap of p orbitals in a continuous manner and preventing the delocalization of π electrons throughout the ring.
Due to the absence of continuous overlap of p...
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...
Carbocations02:10

Carbocations

Carbocations are one of the reaction intermediates formed during several nucleophilic substitutions or elimination reactions. A carbocation is an electron-deficient species with the central carbon atom having six electrons and three bonded atoms. The central carbon in a carbocation is sp2 hybridized with trigonal planar geometry. It has an empty p orbital perpendicular to the plane of the structure that can accept electrons. Thus, carbocations act as strong electrophiles and may react with any...
Nucleophilic Aromatic Substitution: Elimination–Addition01:11

Nucleophilic Aromatic Substitution: Elimination–Addition

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 confirmed through isotopic...
β-Dicarbonyl Compounds via Crossed Claisen Condensations01:18

β-Dicarbonyl Compounds via Crossed Claisen Condensations

Crossed Claisen condensations are base-promoted reactions between two different ester molecules producing β-dicarbonyl compounds. The reaction involving esters, with both containing α hydrogen, results in a mixture of four different products that are difficult to isolate. This reduces the synthetic utility of the reaction.
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction01:16

[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction

The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.

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Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
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Isolating Free Carbenes, their Mixed Dimers and Organic Radicals

Published on: April 19, 2019

A viable anionic N-heterocyclic dicarbene.

Yuzhong Wang1, Yaoming Xie, Mariham Y Abraham

  • 1Department of Chemistry and the Center for Computational Chemistry, The University of Georgia, Athens, Georgia 30602-2556, USA.

Journal of the American Chemical Society
|September 25, 2010
PubMed
Summary

Researchers synthesized the first anionic N-heterocyclic dicarbene, a polymer featuring both normal and abnormal carbene centers. This novel compound was characterized by forming adducts with group 13 Lewis acids.

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Preparation and Use of Carbonyl-decorated Carbenes in the Activation of White Phosphorus
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Preparation and Use of Carbonyl-decorated Carbenes in the Activation of White Phosphorus

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Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions
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Preparation and Use of Carbonyl-decorated Carbenes in the Activation of White Phosphorus

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Area of Science:

  • Organometallic Chemistry
  • Polymer Chemistry
  • Carbene Chemistry

Background:

  • N-heterocyclic carbenes (NHCs) are versatile ligands in organometallic chemistry.
  • Polymeric NHCs offer unique structural and electronic properties.
  • The synthesis of anionic NHCs presents specific challenges.

Purpose of the Study:

  • To synthesize and characterize the first anionic N-heterocyclic dicarbene.
  • To investigate the presence of both normal and abnormal carbene centers within the same imidazole ring.
  • To explore the reactivity of this novel dicarbene with Lewis acids.

Main Methods:

  • Lithiation of an imidazole monocarbene precursor.
  • Polymerization to form the anionic dicarbene.
  • Characterization via formation of group 13 Lewis acid adducts.

Main Results:

  • Successful synthesis of the first anionic N-heterocyclic dicarbene polymer.
  • Demonstration of both normal (C2) and abnormal (C4) carbene centers in the same imidazole ring.
  • Formation of stable adducts with aluminum (AlMe3) and boron (BEt3) Lewis acids, confirming dicarbene nature.

Conclusions:

  • The study reports the first anionic N-heterocyclic dicarbene, a polymeric species.
  • The compound uniquely incorporates both normal and abnormal carbene functionalities.
  • The reactivity with Lewis acids validates its dicarbene character and opens avenues for further applications.