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Related Concept Videos

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: 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 Reactivity: Nucleophilic Radicals01:16

Radical Reactivity: Nucleophilic Radicals

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 instance, consider...
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...
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 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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Related Experiment Video

Updated: May 18, 2026

Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry
09:37

Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry

Published on: October 18, 2019

Radical SAM-dependent carbon insertion into the nitrogenase M-cluster.

Jared A Wiig1, Yilin Hu1, Chi Chung Lee1

  • 1Department of Molecular Biology & Biochemistry, University of California, Irvine 92697-3900.

Science (New York, N.Y.)
|September 29, 2012
PubMed
Summary

The nitrogenase enzyme

Area of Science:

  • Biochemistry
  • Enzymology
  • Bioinorganic Chemistry

Background:

  • Nitrogenase catalyzes biological nitrogen fixation, a crucial process for life.
  • The enzyme's active site, the M-cluster, contains a unique interstitial carbide.
  • The origin and insertion mechanism of this carbide remain largely unknown.

Purpose of the Study:

  • To elucidate the origin of the carbide in the nitrogenase M-cluster.
  • To identify the protein responsible for carbide insertion.
  • To compare the carbon insertion mechanism with related radical SAM enzyme reactions.

Main Methods:

  • Radiolabeling experiments using S-adenosylmethionine (SAM).
  • Deuterium substitution analysis.
  • Analysis of the assembly protein NifB's role.

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Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
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Last Updated: May 18, 2026

Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry
09:37

Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry

Published on: October 18, 2019

A New Approach for the Comparative Analysis of Multiprotein Complexes Based on 15N Metabolic Labeling and Quantitative Mass Spectrometry
08:04

A New Approach for the Comparative Analysis of Multiprotein Complexes Based on 15N Metabolic Labeling and Quantitative Mass Spectrometry

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Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
10:44

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals

Published on: April 19, 2019

Main Results:

  • The carbide in the M-cluster originates from the methyl group of SAM.
  • The assembly protein NifB is responsible for inserting the carbide into the M-cluster.
  • The mechanism shares similarities with RNA methylation by radical SAM enzymes.

Conclusions:

  • The interstitial carbide in nitrogenase originates from SAM and is inserted by NifB.
  • The carbon insertion mechanism by NifB resembles that of radical SAM enzymes involved in RNA methylation.
  • This study provides initial insights into the nitrogenase mechanism and the role of the interstitial carbide.