Scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory are using it to measure how an atom’s unpaired electrons on one end of a molecule can drive chemical reactions on the other side of the molecule. It was helpful. As explained in a recently published paper, Journal of the American Chemical Societythis study, in collaboration with Princeton University, shows how these so-called free-radical-containing molecules can be used in an entirely new class of reactions.
“Most reactions involved Free radicals The Princeton University team had become experts in using free radicals for a variety of synthetic applications, including upcycling polymers. However, they suspected that free radicals might affect the reactivity of other parts of the molecule, pulling electrons away from more distant locations.
“Our measurements show that these radicals can exert a powerful ‘electron-withdrawing’ effect that makes other parts of the molecule more reactive,” Byrd said.
The Princeton team showed how its long-range pulls overcome energy barriers and bring together things that otherwise wouldn’t react moleculewhich may lead to new approaches to organic molecule synthesis.
combination of functions
The research focused on bio-inspired photo-escalation chemistry (BioLEC), combining resources from the DOE Energy Frontier Research Center (EFRC) led by Princeton. This collaboration brings together leading synthetic chemists and groups with advanced spectroscopic techniques to study reactions.
Robert Knowles, who led Princeton’s role in the study, said, “This project will allow the team to combine BioLEC’s expertise to quantify the key physical properties of these radical species and the resulting synthetic methodology. This is an example that made it possible to design
A major contribution of the Brookhaven team is a technique called pulse radiolysis. This is only available in Brookhaven and one other location in the US.
“We use the Laser Electron Accelerator Facility (LEAF), part of the Center for Energy Research Accelerator (ACER) in the Department of Chemistry, Brookhaven, to generate powerful, high-energy electron pulses,” said Bird. explained. “These pulses can add or subtract electrons from molecules to create reactive species that are difficult to create with other techniques, such as short-lived reactive intermediates. You can step in and watch what happens.”
In the current study, the team used pulse radiolysis to generate molecules with radicals centered around oxygen and measured the ‘electron withdrawal’ effect on the other side of the molecule. They measured electron attraction by tracking how well the opposite oxygen attracts protons. Byrd explained that the stronger the attraction from the radical, the more acidic the solution had to be in order for the protons to bind to the molecule.
Brookhaven scientists found that acidity must be high to allow proton capture. That is, the oxygen radical was a very strong electron-withdrawing group. This was good news for his Princeton team. They next demonstrated that they could take advantage of the ‘electron-withdrawing’ effect of oxygen radicals by making some of the normally inert molecules more chemically reactive.
“Oxygen radicals cause a temporary ‘polarity reversal’ in the molecule, causing electrons that would normally stay on the far side to move to the opposite side. radical It’s to make the ‘far’ side more reactive,” Byrd explained.
These discoveries enabled new substitution reactions with phenol-based starting materials to make more complex phenolic products.
“This is a great example of how the technique of pulse radiolysis can be applied to cutting-edge scientific problems,” said Byrd. We are delighted to welcome Nick Singh and look forward to many more collaborative projects in this second phase of BioLEC and what new problems we can explore using pulse radiolysis. .”
For more information:
Nick Y. Shin et al., Radicals as Exceptional Electron-Withdrawing Groups: Nucleophilic Aromatic Substitution of Halophenols Via Homolysis-enabled Electronic Activation, Journal of the American Chemical Society (2022). DOI: 10.1021/jacs.2c10296
Brookhaven National Laboratory
Quote: A Radical New Approach in Synthetic Chemistry (23 November 2022), from https://phys.org/news/2022-11-radical-approach-synthetic-chemistry.html on 23 November 2022 acquisition
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