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Radical Formation: Addition00:47

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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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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.
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4.4K
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Conformation-Variable [7]Annulenyl Radicals.

Guantao Yang1, Lingfang Chen2,3, Zhizhe Liu1

  • 1Beijing National Laboratory For Molecular Sciences, Centre For the Soft Matter Science and Engineering, College of Chemistry, the Key Laboratory of Polymer Chemistry and Physics of the Ministry of Education, Peking University, Beijing, P. R. China.

Chemistry (Weinheim an Der Bergstrasse, Germany)
|January 16, 2026
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Summary
This summary is machine-generated.

Researchers synthesized novel benzo-fused [7]annulenyl radicals. Molecular structure significantly impacts radical stability and spin distribution, with planar structures and specific substituents enhancing persistence.

Keywords:
heptagon‐embedded radicalorganic radicalstability

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Area of Science:

  • Organic Chemistry
  • Materials Science
  • Physical Chemistry

Background:

  • Benzo-fused [7]annulenyl radicals are of interest due to their unique electronic and structural properties.
  • Understanding the relationship between molecular structure and radical stability is crucial for designing new materials.

Purpose of the Study:

  • To synthesize and investigate a series of benzo-fused [7]annulenyl radical derivatives.
  • To elucidate how variations in molecular structure affect spin distribution and radical persistence.

Main Methods:

  • Synthesis of novel benzo-fused [7]annulenyl radical derivatives.
  • Electron Paramagnetic Resonance (EPR) spectroscopy to analyze spin distribution.
  • Computational chemistry methods to support experimental findings.

Main Results:

  • A planar dibenzo[a,d][7]annulenyl skeleton with delocalized spin was identified for unsubstituted radicals.
  • Radical persistence varied with substituents; a triisopropylphenyl-substituted radical showed a half-lifetime of 23 hours.
  • Substituents at C10 improved stability but induced slight bending, while tribenzo[a,c,e][7]annulenyl radicals showed lower stability due to nonplanar conformations.
  • Attachment of an anthryl group at C9 induced a conformational change and spin relocation to the anthrylene unit.

Conclusions:

  • Molecular structure, particularly planarity and steric hindrance, critically influences the stability and spin properties of benzo-fused [7]annulenyl radicals.
  • Strategic substitution can enhance radical persistence, but nonplanar conformations can significantly reduce stability and alter spin localization.
  • Conformational flexibility and substituent effects offer pathways to tune the properties of these radical systems.