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Radical Reactivity: Overview01:11

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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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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: Steric Effects01:10

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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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Chain-growth or addition polymerization is successive addition reactions of monomers with a polymer chain. In radical chain-growth polymerization, the reaction proceeds via a free-radical intermediate. The free radical is formed from radical initiators, which spontaneously generate free radicals by homolytic fission. Organic peroxides (such as dibenzoyl peroxide, as shown in Figure 1) or azo compounds are popular radical initiators. A low concentration ratio of radical initiator to monomer is...
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Radical Reactivity: Nucleophilic Radicals01:16

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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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The conversion of alkenes to macromolecules called polymers is a reaction of high commercial importance. The structure of the polymer is defined by a repeating unit, while the terminal groups are considered insignificant. The average degree of polymerization represents the number of repeating units in the polymer molecule and is denoted by the subscript n.
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Fluorenyl Based Macrocyclic Polyradicaloids.

Xuefeng Lu1, Sangsu Lee2, Yongseok Hong2

  • 1Department of Chemistry, National University of Singapore , 3 Science Drive 3, 117543 Singapore.

Journal of the American Chemical Society
|August 26, 2017
PubMed
Summary
This summary is machine-generated.

Stable macrocyclic polyradicaloids with tunable spin interactions were synthesized. Geometry significantly impacts their electronic and optical properties, with some exhibiting antiaromaticity.

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Area of Science:

  • Organic Chemistry
  • Materials Science
  • Supramolecular Chemistry

Background:

  • Controlling intramolecular spin-spin interactions in polyradicaloids is crucial for developing advanced organic materials.
  • Stable, well-defined macrocyclic polyradicaloids are challenging to synthesize and characterize.

Purpose of the Study:

  • To synthesize and characterize novel fluorenyl-based macrocyclic polyradicaloids.
  • To investigate the effect of molecular geometry, including the presence of ethynylene spacers, on their electronic and magnetic properties.
  • To compare the properties of macrocyclic polyradicaloids with their linear counterparts.

Main Methods:

  • Development of three distinct synthetic routes for macrocyclic polyradicaloids.
  • Purification using standard silica gel column chromatography.
  • Computational analysis using restricted active space spin-flip (RASSF) method.
  • Characterization of magnetic properties using superconducting quantum interference device (SQUID) measurements.
  • Evaluation of optical and electrochemical properties.

Main Results:

  • Successful synthesis of two series of stable fluorenyl-based macrocyclic polyradicaloids (FR-MCn and MC-FnAn).
  • Calculated moderate polyradical character due to antiferromagnetic spin-spin interactions.
  • Demonstrated significant influence of geometry (distortional angle, ethynylene spacer) on polyradical character, excitation energies, and absorption properties.
  • Identified global antiaromatic character in macrocyclic tetramers (FR-MC4 and MC-F4A4) arising from cyclic π-conjugation.

Conclusions:

  • The synthetic strategies provide access to stable macrocyclic polyradicaloids under ambient conditions.
  • Molecular geometry is a key determinant of the electronic, optical, and magnetic properties of these systems.
  • The discovery of antiaromaticity in specific macrocyclic structures opens new avenues for exploring electronic materials.