Related Experiment Video
Updated: Nov 30, 2025
10:44
Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
11.3K
Dynamic solvent effects in radical-radical coupling reactions: an almost bottleable localised singlet diradical
Rikuo Akisaka1, Yasushi Ohga, Manabu Abe
1Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan. mabe@hiroshima-u.ac.jp.
Physical Chemistry Chemical Physics : PCCP
|November 13, 2020
Summary
Researchers investigated long-lived singlet diradicals, crucial in chemical reactions. They found solvent effects control radical coupling, achieving a stable diradical with a ~2-second lifetime at room temperature.
Area of Science:
- Chemical Dynamics
- Organic Chemistry
- Physical Chemistry
Background:
- Singlet diradicals are vital intermediates in bond homolysis and chemical reactions.
- Studying diradical reaction dynamics is challenging due to rapid bond formation, even at low temperatures.
Purpose of the Study:
- To investigate the influence of solvent and pressure on the lifetimes of singlet diradicals.
- To understand how solvent dynamics affect radical-radical coupling rates.
- To synthesize and characterize a stable, long-lived singlet diradical.
Main Methods:
- Synthesis of singlet diradicals with bulky substituents.
- Variable temperature and pressure studies in different solvent environments.
- Spectroscopic analysis to determine diradical lifetimes and properties.
Main Results:
- Solvent dynamics were found to significantly control the rate constant of radical-radical coupling.
- A remarkably stable singlet diradical, nearly isolable ('bottleable'), was achieved.
- The diradical exhibited a lifetime of approximately 2 seconds at 293 K.
Conclusions:
- Solvent effects are a key factor in controlling the stability and reactivity of singlet diradicals.
- The development of long-lived diradicals opens new avenues for studying reaction mechanisms.
- This work demonstrates the potential for designing and stabilizing reactive intermediates.
Related Concept Videos
01:11Radical Reactivity: Overview
2.5K
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...
2.5K
01:16Radical Reactivity: Nucleophilic Radicals
2.4K
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...
2.4K
01:33Radical Reactivity: Intramolecular vs Intermolecular
2.0K
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...
2.0K
01:10Radical Reactivity: Steric Effects
2.2K
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...
Along with electronic...
2.2K
00:47Radical Formation: Addition
2.0K
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...
Similar to charge conservation in chemical reactions, spin conservation is implicit for radical reactions. Accordingly, the product formed must possess an...
2.0K
01:20Radical Reactivity: Concentration Effects
1.7K
In a radical reaction, the concentration of starting materials governs the selectivity of a radical. For example, the reaction between an alkyl halide and an alkene, in the presence of tin hydride and AIBN, begins with the generation of a tin radical. The generated radical then abstracts halogen from the alkyl halide, producing an alkyl radical. This alkyl radical can either react with tin hydride, yielding an alkane, or add to an alkene, generating a nitrile-stabilized radical, eventually...
1.7K