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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...
Radicals: Electronic Structure and Geometry01:07

Radicals: Electronic Structure and Geometry

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.
Accordingly, the structure of a trivalent radical lies between the geometries of carbocations and carbanions. An sp2-hybridized carbocation is trigonal planar, while an sp3-hybridized carbanion is trigonal pyramidal. Here, the difference in geometry is...
π Molecular Orbitals of the Allyl Radical01:27

π Molecular Orbitals of the Allyl Radical

Allyl radicals are three-carbon conjugated systems. They are readily formed as intermediates in halogenation reactions of alkenes involving the addition of halogen to the allylic carbon instead of the double bond. As seen in allyl cations and anions, each of the three sp2-hybridized carbon atoms in allyl radicals has an unhybridized p orbital. These orbitals combine to give three π molecular orbitals.
The allyl systems have identical molecular orbitals but differ in the number of π electrons.
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 Halogenation: Stereochemistry01:33

Radical Halogenation: Stereochemistry

Stereochemistry is the study of the different spatial arrangements of atoms in a given molecule. The stereochemistry of radical halogenations can be understood from three different situations:
Halogenation to form a new chiral center:

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Exploring the Radical Nature of a Carbon Surface by Electron Paramagnetic Resonance and a Calibrated Gas Flow
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Published on: April 24, 2014

Switching radical stability by pH-induced orbital conversion.

Ganna Gryn'ova1, David L Marshall, Stephen J Blanksby

  • 1Australian Research Council Centre of Excellence for Free Radical Chemistry and Biotechnology, Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory 0200, Australia.

Nature Chemistry
|May 23, 2013
PubMed
Summary

This study reveals pH-switchable orbital conversion in distonic radical anions, significantly enhancing radical stability and acidity. This discovery opens new industrial applications, like pH-controlled polymerization.

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Area of Science:

  • Theoretical and Experimental Chemistry
  • Physical Chemistry
  • Organic Chemistry

Background:

  • Typically, the singly occupied molecular orbital (SOMO) is the highest-energy occupied molecular orbital (HOMO) in radicals.
  • A rare phenomenon, SOMO-HOMO energy-level conversion, has been observed in specific compounds.

Purpose of the Study:

  • To significantly expand the scope of SOMO-HOMO energy-level conversion.
  • To investigate its occurrence in distonic radical anions with stabilized radicals and negative charges.
  • To explore the implications of pH-induced orbital configuration switching.

Main Methods:

  • Theoretical calculations to model electronic structures.
  • Experimental validation of theoretical predictions.
  • Investigation of distonic radical anions containing aminoxyl, peroxyl, or aminyl radicals and carboxylate, phosphate, or sulfate charges.

Main Results:

  • SOMO-HOMO energy-level conversion is shown to occur in a wide range of distonic radical anions.
  • Protonation of the anionic fragment restores the regular orbital order, enabling pH-switchable configurations.
  • These distonic radical anions exhibit significantly enhanced radical stability and proton acidity.

Conclusions:

  • The study demonstrates a broad applicability of SOMO-HOMO energy-level conversion in distonic radical anions.
  • pH-induced orbital conversion offers a mechanism to modulate radical stability by 3-4 orders of magnitude.
  • Potential industrial applications include pH-switchable nitroxide-mediated polymerization and biological exploitation.