researchers in Brookhaven National Laboratory The U.S. Department of Energy (DOE) helped assess how an unpaired electron in an atom on one end of a molecule affects chemical reactivity on the other side of the molecule.
This work, conducted in collaboration with Princeton University, is described in a recently published study. Journal of the American Chemical SocietyIt shows how molecules containing these “free radicals” can be used in an entirely new class of reactions.
Most reactions involving free radicals occur at unpaired electron sites.
Matthew Bird, Study Co-Corresponding Author and Associate Chemist, Chemistry Division, Brookhaven National Laboratory
A team at Princeton University had mastered the use of free radicals in a number of synthetic processes, including polymer recycling. However, they question whether free radicals can also affect the reactivity of other molecular regions, drawing electrons away from these further reached regions.
Byrd added:Our measurements show that these radicals can exert a strong ‘electron-withdrawing’ effect making other parts of the molecule more reactive.”
A team from Princeton University has shown how that long-range pull can overcome energy barriers and bind molecules that normally don’t react with each other. This may open the door to new ways to synthesize organic molecules.
combination of functions
This research utilized a combination of resources from the DOE Energy Frontier Research Center (EFRC), led by Princeton.
Leading experts in synthetic chemistry work with organizations that have state-of-the-art spectroscopic methods to study reactions. Recently, he also received four years of funding.
This project is an example of how BioLEC’s combined expertise has enabled the team to quantify key physical properties of these radical species and design the resulting synthetic methodology.
Robert Knowles, Professor, Department of Chemistry, Princeton University
A major contribution of the Brookhaven team is a procedure called pulse radiolysis, which is only performed at Brookhaven and one other location in the United States.
“The Laser Electron Accelerator Facility (LEAF), part of the Center for Energy Research Accelerator (ACER) in the Department of Chemistry, Brookhaven, is used to generate powerful high-energy electron pulses. These pulses can add or remove electrons from molecules to create reactive species, such as short-lived reactive intermediates, that are difficult to create with other techniques.This technique allows you to step into part of the reaction and watch what happensmore birds were added.
For their current study, the team used pulsed radiolysis to create molecules with oxygen-centered radicals and observed an ‘electron-withdrawing’ effect on the other side of the molecule.
By observing how many protons the oxygen on the other side attracts, positively charged ions bounce around in solution and the attraction of electrons could be measured. According to Byrd, the stronger the attraction of the radical, the more acidic the solution must be in order for the proton to bind to the molecule.
Brookhaven researchers found that high acidity is required for proton capture. This indicates that the oxygen radical is a very strong electron-withdrawing group. The Princeton team was thrilled to hear that.
They next showed that the ‘electron-withdrawing’ effect of oxygen radicals can be exploited by modifying the typically chemically inert part of the molecule to be more reactive.
Byrd further states:Oxygen radicals cause a temporary “polarity reversal” in the molecule. This causes electrons that would normally stay on the far side to move towards the radical, making the “far” side more reactive.”
These findings have made it possible to create more complex phenolic products using novel substitution reactions on phenol-based starting materials.
“This is a great example of how the technique of pulse radiolysis can be applied to cutting-edge scientific problems. For this collaboration, we are pleased to welcome his Nick Shin, an outstanding graduate student from the Knowles group. This he is looking forward to more collaborative projects in the second phase of BioLEC to see what new problems can be explored using pulse radiolysis.added Byrd.
The DOE Office of Science (BES) funded the EFRC at Princeton, and the Brookhaven Laboratory participated in the project. The National Institutes of Health provided additional funding to Princeton for synthetic work.
The U.S. Department of Energy’s Office of Science funds the Brookhaven National Laboratory. The Office of Science addresses some of today’s most important problems and is the single largest supporter of basic research in the physical sciences of the United States.
Singh, New York, and others. (2022) Radicals as Exceptional Electron-Withdrawing Groups: Nucleophilic Aromatic Substitution of Halophenols by Homolysis-Compatible Electron Activation. Journal of the American Chemical Society. doi:10.1021/jacs.2c10296.