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Radical Reactivity: Steric Effects01:10

Radical Reactivity: Steric Effects

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The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
Along with electronic...
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Radical Reactivity: Overview01:11

Radical Reactivity: Overview

2.3K
Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired...
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Radical Reactivity: Electrophilic Radicals01:02

Radical Reactivity: Electrophilic Radicals

2.1K
Radicals adjacent to electron‐withdrawing groups are called electrophilic radicals. These radicals readily react with nucleophilic alkenes. For example, the malonate radical, in which the radical center is flanked by two electron‐withdrawing groups, reacts readily with butyl vinyl ether, which consists of an electron‐donating oxygen substituent. The reaction between electrophilic malonate radical and nucleophilic vinyl ether is favored because the radical has a...
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Radical Reactivity: Nucleophilic Radicals01:16

Radical Reactivity: Nucleophilic Radicals

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Radicals adjacent to electron-donating groups are called nucleophilic radicals. These radicals readily react with electrophilic alkenes. The SOMO–LUMO interactions are the driving force for the reaction, where the high-energy SOMO of the electron-rich, nucleophilic radicals interacts with the low-energy LUMO of the electron-deficient, electrophilic alkenes. Such SOMO–LUMO interactions are the basis of reactive radical traps, affecting the selectivity in radical reactions. For...
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Radicals: Electronic Structure and Geometry01:07

Radicals: Electronic Structure and Geometry

4.5K
This lesson delves into the geometry of a radical, which is influenced by the electronic structure of the molecule. The principle is similar to that of a lone pair, where the unpaired electron influences the geometry at the radical center.
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Radical Formation: Homolysis00:54

Radical Formation: Homolysis

4.0K
A bond is formed between two atoms by sharing two electrons. When this bond is broken by supplying sufficient energy, either two electrons can be taken up by one atom forming ions by the cleavage called heterolysis, or the two electrons are shared by two atoms, with one each creating radicals by the cleavage called homolysis.
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Related Experiment Video

Updated: Nov 2, 2025

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

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Persistent, highly localized, and tunable [4]helicene radicals.

Aslam C Shaikh1, Jules Moutet1, José M Veleta1

  • 1Department of Chemistry and Biochemistry, University of Arizona Tucson AZ USA tgianetti@arizona.edu.

Chemical Science
|June 14, 2021
PubMed
Summary

Stable neutral quinolinoacridine radicals were synthesized and characterized. These helical molecules exhibit significant spin density localization, enabling unique reversible oxidation upon air exposure for potential optoelectronic applications.

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Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development
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Area of Science:

  • Organic Chemistry
  • Materials Science
  • Catalysis

Background:

  • Persistent organic radicals are crucial in catalysis and materials science.
  • Helical molecules, specifically organic radicals, are of significant interest for advanced optoelectronic and spintronic materials.
  • Development of stable and tunable organic radicals is essential for novel material applications.

Purpose of the Study:

  • To synthesize easily tunable and stable neutral quinolinoacridine radicals.
  • To investigate the structural and electronic properties of these novel [4]helicene radicals.
  • To explore the reactivity of these radicals, particularly their interaction with molecular oxygen.

Main Methods:

  • Chemical reduction of quinolinoacridinium cation analogs under anaerobic conditions.
  • Structural determination using X-ray crystallography.
  • Electronic property analysis via Density Functional Theory (DFT) calculations and Electron Paramagnetic Resonance (EPR) spectroscopy.
  • Reactivity studies using UV-Vis spectroscopy.

Main Results:

  • Successfully synthesized stable neutral [4]helicene quinolinoacridine radicals.
  • X-ray crystallography confirmed the helical structures.
  • DFT calculations and EPR measurements revealed over 40% spin density localized at the central carbon atom, irrespective of structural modifications.
  • Demonstrated reversible oxidation to the cation upon exposure to air.

Conclusions:

  • The synthesized [4]helicene radicals are stable, tunable, and possess unique spin density localization.
  • The charge localization facilitates an unusual reversible oxidation with molecular oxygen.
  • These findings highlight the potential of quinolinoacridine radicals in developing novel functional materials for optoelectronics and spintronics.