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Related Concept Videos

Radical Reactivity: Overview01:11

Radical Reactivity: Overview

2.2K
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...
2.2K
Radical Formation: Overview01:03

Radical Formation: Overview

2.2K
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...
2.2K
Radical Formation: Addition00:47

Radical Formation: Addition

1.9K
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...
1.9K
Radical Reactivity: Electrophilic Radicals01:02

Radical Reactivity: Electrophilic Radicals

2.0K
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...
2.0K
Radical Formation: Elimination00:51

Radical Formation: Elimination

1.9K
Another method of radical formation is the elimination process. It is the opposite of the addition route and is driven by the instability of the radical. For example, as depicted in Figure 1, dibenzoyl peroxide yields a pair of unstable radicals upon homolysis. Given its instability, this radical spontaneously undergoes elimination via a C–C bond cleavage to form a relatively more stable phenyl radical. The mechanism involves cleavage of the bond between the α and β positions...
1.9K
Radicals: Electronic Structure and Geometry01:07

Radicals: Electronic Structure and Geometry

4.3K
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...
4.3K

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Related Experiment Video

Updated: Oct 8, 2025

Exploring the Radical Nature of a Carbon Surface by Electron Paramagnetic Resonance and a Calibrated Gas Flow
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A radical approach to radicals.

Youjia Liu1, Malgorzata Biczysko1, Nigel W Moriarty2

  • 1International Center for Quantum and Molecular Structures, Shanghai University, Shanghai 200444, People's Republic of China.

Acta Crystallographica. Section D, Structural Biology
|January 4, 2022
PubMed
Summary

Nitroxide radicals, used as spin labels in proteins, were refined using quantum calculations. This method improved structural accuracy for these unusual radical compounds in crystallographic data.

Keywords:
chemical radicalsligand restraintsmacromolecular refinementnitroxidesquantum chemistryspin labelling

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Area of Science:

  • Biochemistry
  • Structural Biology
  • Computational Chemistry

Background:

  • Nitroxide radicals possess unique electronic properties, making them valuable as spin labels for studying protein structure and dynamics via electron paramagnetic resonance spectroscopy.
  • Incorporating nitroxides into proteins for site-directed spin labeling creates complex protein-ligand models.
  • Macromolecular crystallography often yields inaccurate structural information for nitroxides due to their unusual chemical nature as radicals.

Purpose of the Study:

  • To improve the accuracy of structural data for nitroxide radicals within protein crystallographic models.
  • To develop a method for refining the structural parameters of nitroxide ligands (MTN) using computational chemistry.

Main Methods:

  • Re-refinement of proteins containing the nitroxide radical (MTN) using crystallographic data.
  • Definition of ideal structural parameters for the MTN ligand based on quantum-chemical calculations.

Main Results:

  • The applied refinement procedure successfully improved the geometric accuracy of the MTN ligand.
  • The refined structures maintained a high degree of agreement with the experimental crystallographic data.
  • This approach addresses the challenges of incorporating radical species into macromolecular models.

Conclusions:

  • Quantum-chemical calculations can provide accurate ideal structural parameters for nitroxide radicals.
  • Re-refining protein structures with these calculated parameters enhances the quality of crystallographic models containing nitroxides.
  • This methodology offers a pathway to more reliable structural insights into proteins modified with spin labels.