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Related Concept Videos

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

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Published on: April 19, 2019

Dynamic nuclear polarization with a rigid biradical.

Yoh Matsuki1, Thorsten Maly, Olivier Ouari

  • 1Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

Angewandte Chemie (International Ed. in English)
|June 4, 2009
PubMed
Summary

A novel polarizing agent featuring two TEMPO moieties on a rigid spiro tether significantly enhances Nuclear Magnetic Resonance (NMR) signal intensities by 1.4 times compared to flexible tether agents.

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Last Updated: Jun 22, 2026

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Area of Science:

  • Chemistry
  • Biophysics
  • Materials Science

Background:

  • Dynamic Nuclear Polarization (DNP) enhances NMR sensitivity.
  • Existing polarizing agents like TOTAPOL have limitations.
  • Development of advanced polarizing agents is crucial for DNP applications.

Purpose of the Study:

  • Introduce a new polarizing agent with improved DNP performance.
  • Evaluate the efficiency of the novel agent compared to existing ones.
  • Demonstrate the benefits of a rigid spiro tether for TEMPO-based agents.

Main Methods:

  • Synthesis of a novel biradical agent with two TEMPO moieties linked by a rigid spiro tether.
  • Dynamic Nuclear Polarization (DNP) experiments.
  • Nuclear Magnetic Resonance (NMR) spectroscopy for signal intensity measurements.

Main Results:

  • The novel spiro tethered TEMPO-based agent demonstrated superior performance in DNP.
  • NMR signal intensities were enhanced by a factor of 1.4 compared to TOTAPOL.
  • The rigid tether structure contributes to the enhanced polarizing efficiency.

Conclusions:

  • The new spiro tethered agent represents a significant advancement in DNP polarizing agents.
  • This agent offers improved sensitivity for NMR spectroscopy.
  • The rigid tether design is a promising strategy for future DNP agent development.