“Most reactions involving free radicals occur at the site of an unpaired electron,” explained Matthew Bird, a chemist at the Brookhaven Institute and one of the paper’s co-corresponding authors. The Princeton team had become experts in using free radicals for a variety of synthetic applications, including upcycling polymers. However, they suspected that free radicals might also 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.

A team from Princeton University demonstrates how that long-range pull overcomes energy barriers and assembles otherwise unreactive molecules, potentially leading 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. That funding was recently renewed for another four years.

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). The Laser Electron Accelerator Facility (LEAF) is part of the Center for Energy Research Accelerator (ACER) in the Department of Chemistry, Brookhaven, where powerful high-energy It generates an electronic pulse,” 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 toward the radical, making the ‘far’ side more reactive.” explained Byrd.

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. .”

The role of the Brookhaven Laboratory in this work and the EFRC at Princeton was funded by the DOE Office for Science (BES). Princeton received additional funding for synthetic work from the National Institutes of Health.