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Related Concept Videos

Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

3.2K
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...
3.2K
Aromatic Hydrocarbon Anions: Structural Overview01:18

Aromatic Hydrocarbon Anions: Structural Overview

3.2K
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...
3.2K
Valence Bond Theory02:42

Valence Bond Theory

9.9K
Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
9.9K
Basicity of Heterocyclic Aromatic Amines01:25

Basicity of Heterocyclic Aromatic Amines

6.5K
Heterocyclic amines, where the N atom is a part of an alicyclic system, are similar in basicity to alkylamines. Interestingly, the heterocyclic amine having a nitrogen atom as part of an aromatic ring has much less basicity than its corresponding alicyclic counterpart. For this reason, as presented in Figure 1, piperidine (pKb = 2.8) is significantly more basic than pyridine (pKb = 8.8).
6.5K
Crystal Field Theory - Tetrahedral and Square Planar Complexes02:46

Crystal Field Theory - Tetrahedral and Square Planar Complexes

45.5K
Tetrahedral Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
45.5K
Diazonium Group Substitution: –OH and –H01:19

Diazonium Group Substitution: –OH and –H

3.0K
Nitrous acid, a weak acid, is prepared in situ via the reaction of sodium nitrite with a strong acid under cold conditions. This nitrous acid prepared in situ reacts with primary arylamines to form arenediazonium salts. Such reactions are known as diazotization reactions. As shown in Figure 1, the formation of arenediazonium salts begins with the decomposition of nitrous acid in an acidic solution to give nitrosonium ions.
3.0K

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Updated: Oct 28, 2025

Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
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Does the 2,6-didehydropyridinium cation exist?

Bartłomiej J Jankiewicz1,2, Nelson R Vinueza1, Lindsey M Kirkpatrick1

  • 1B. J. Jankiewicz, N. R. Vinueza, L. M. Kirkpatrick, V. A. Gallardo, G. Li, J. J. Nash, H. I. Kenttämaa Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907-2084, USA.

Journal of Physical Organic Chemistry
|July 15, 2021
PubMed
Summary
This summary is machine-generated.

Researchers generated and studied protonated 2,6-didehydropyridine, a reactive intermediate. The singlet and triplet states exhibited distinct chemical properties and reactivity, offering new insights into biradical chemistry.

Keywords:
DidehydrobenzeneFT-ICRbiradicalsion-molecule reactionsreactive intermediates

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Area of Science:

  • Organic Chemistry
  • Physical Chemistry
  • Chemical Physics

Background:

  • Reactive intermediates are crucial in chemical and biochemical processes.
  • Aromatic σ,σ-biradicals, like those from enediyne antibiotics, cleave DNA but are difficult to study due to high reactivity.
  • 2,6-didehydropyridine has been a long-speculated aromatic biradical, lacking definitive proof of generation.

Purpose of the Study:

  • To successfully generate protonated 2,6-didehydropyridine.
  • To examine the chemical properties and reactivity of this biradical in the gas phase.
  • To differentiate the behavior of its singlet and triplet states.

Main Methods:

  • Generation of protonated 2,6-didehydropyridine.
  • Investigation of gas-phase chemical properties using Fourier transform ion cyclotron resonance mass spectrometry.

Main Results:

  • Successful generation of protonated 2,6-didehydropyridine.
  • Evidence for a mixture of singlet (ground) and triplet (excited) states.
  • The triplet state exhibited greater Brønsted acidity and radical reactivity compared to the singlet state.

Conclusions:

  • The study provides the first definitive proof of 2,6-didehydropyridine generation.
  • Singlet and triplet states of 2,6-didehydropyridinium cations display distinct reactivity.
  • Findings advance the understanding of reactive biradical intermediates and their properties.