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Related Concept Videos

Radical Reactivity: Steric Effects01:10

Radical Reactivity: Steric Effects

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 factors, steric factors also account...
Radical Reactivity: Overview01:11

Radical Reactivity: Overview

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 molecule. These three...
Radical Formation: Overview01:03

Radical Formation: Overview

A bond can be broken either by heterolytic bond cleavage to form ions or homolytic bond cleavage to yield radicals. A fishhook arrow is used to represent the motion of a single electron in homolytic bond cleavage. There are two main sources from which radicals can be formed:
Radicals from spin-paired molecules:
Radicals can be obtained from spin-paired molecules either by homolysis or electron transfer. While two radicals are formed in the former, an electron is added in the latter, also known...
Radical Formation: Addition00:47

Radical Formation: Addition

Radicals can be formed by adding a radical to a spin-paired molecule. This is typically observed with unsaturated species, where the addition of a radical across the π bond leads to the production of a new radical by dissolving the π bond. For example, the addition of a Br radical to an alkene yields a carbon-centered radical.
Similar to charge conservation in chemical reactions, spin conservation is implicit for radical reactions. Accordingly, the product formed must possess an unpaired...
Radical Formation: Homolysis00:54

Radical Formation: Homolysis

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.
Radical Reactivity: Intramolecular vs Intermolecular01:33

Radical Reactivity: Intramolecular vs Intermolecular

Radical reactions can occur either intermolecularly or intramolecularly. In an intermolecular radical reaction, a nucleophilic radical adds to an electrophilic alkene or vice versa. In such reactions, the radical and generally the alkene, which is also called the radical trap, are two different molecules. Additionally, for such intermolecular reactions to occur, the radical trap must be active, present in an excess concentration, and the radical starting material must have a weak carbon–halogen...

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Exploring the Radical Nature of a Carbon Surface by Electron Paramagnetic Resonance and a Calibrated Gas Flow
10:34

Exploring the Radical Nature of a Carbon Surface by Electron Paramagnetic Resonance and a Calibrated Gas Flow

Published on: April 24, 2014

Mechanical bond-induced radical stabilization.

Hao Li1, Zhixue Zhu, Albert C Fahrenbach

  • 1Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States.

Journal of the American Chemical Society
|November 21, 2012
PubMed
Summary
This summary is machine-generated.

Researchers synthesized novel [2]rotaxanes with stabilized radical cations. These molecular machines exhibit tunable shuttling barriers and potential for paramagnetic materials and conductive devices.

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Area of Science:

  • Supramolecular Chemistry
  • Materials Science
  • Organic Chemistry

Background:

  • Rotaxanes are mechanically interlocked molecules with potential applications in molecular devices.
  • Stabilized radical cations are crucial building blocks for advanced materials.
  • 4,4'-bipyridinium (BIPY(2+)) units are common components in redox-active systems.

Purpose of the Study:

  • To synthesize a homologous series of [2]rotaxanes featuring cyclobis(paraquat-p-phenylene) (CBPQT(4+)) and varying oligomethylene chain lengths on 4,4'-bipyridinium (BIPY(2+)) dumbbell components.
  • To investigate the electrochemical properties and stability of the resulting BIPY(•+) radical cations.
  • To explore the relationship between molecular structure and the dynamics of ring shuttling.

Main Methods:

  • Synthesis utilizing radical templation and copper-free azide-alkyne cycloaddition reactions.
  • Characterization by cyclic voltammetry, UV/vis spectroscopy, mass spectrometry, and 1H NMR spectroscopy.

Main Results:

  • Successful synthesis of a series of [2]rotaxanes with stabilized BIPY(•+) radical cations, resistant to oxidation.
  • Observation of enhanced Coulombic repulsion in oxidized forms, destabilizing ground-state co-conformations.
  • Smallest [2]rotaxane exists as a monoradical under ambient conditions.
  • Linear increase in activation energy barriers for ring shuttling with increasing chain length.

Conclusions:

  • A novel method for producing highly stabilized BIPY(•+) radical cations has been developed.
  • The synthesized [2]rotaxanes offer tunable molecular dynamics for potential applications.
  • These findings open avenues for constructing paramagnetic materials and conductive molecular electronic devices.