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Chemists for the first time rearranged atomic bonds in a single molecule

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If chemists were building cars, they would fill a factory with car parts, set it on fire, and sift the ash into pieces that now vaguely resembled a car.

When you’re dealing with atom-sized car parts, this is a perfectly reasonable process. However, chemists are looking for ways to reduce waste and make reactions more accurate.

Chemical engineering has taken a step forward: researchers at the University of Santiago de Compostela in Spain, the University of Regensburg in Germany and IBM Research Europe have made a single molecule go through a series of transformations with a tiny jolt of voltage.

Typically, chemists achieve precision in reactions by tweaking parameters such as pH, adding or removing available proton donors to control how molecules can trade or exchange electrons to form their bonds.

“However, by these means, the reaction conditions are altered to such an extent that the underlying mechanisms governing selectivity often remain elusive,” the researchers note in their report, published in the journal. The science.

In other words, the complexity of the forces at work pushing and pulling a large organic molecule can make it difficult to accurately measure what happens at each bond.

The team started with a substance called 5,6,11,12-tetrachlorotetracene (with the formula C18H8Cl4), a carbon-based molecule that looks like a row of four honeycombs surrounded by four chlorine atoms hovering around like hungry bees.

By gluing a thin layer of material onto a cold, salt-coated piece of copper, the researchers chased away the chloride bees, leaving behind a handful of excitable carbon atoms that hold unpaired electrons in a series of related structures.

A single molecule converted to isomers (Alabugin and Hu, Nauka, 2022)

Two of these electrons have happily reunited with each other in some structures, reconfiguring the overall honeycomb shape of the molecule. The second pair also sought to connect not only with each other, but with any other available electron that might buzz along their path.

Ordinarily, this wobbly structure would be short-lived, as the remaining electrons would also marry each other. But the researchers found that this particular system was not common.

With a slight jolt of voltage from an atom-sized stun gun, they showed that they could force one molecule to fuse this second pair of electrons in such a way that four cells would shift towards the so-called bent alkyne.

When shaken a little less vigorously, these electrons paired differently, distorting the structure in a completely different way, into what is known as a cyclobutadiene ring.

Each product was then returned to its original state by a pulse of electrons, ready to flip again at any moment.

By causing a single molecule to deform into different shapes, or isomers, using precise voltages and currents, researchers could gain insight into the behavior of its electrons, as well as the stability and preferred configurations of organic compounds.

From here, one could shorten the search for catalysts that could push the large-scale reaction of countless molecules in one direction, making the reaction more specific.

Previous studies have used similar techniques to visualize the reconfigurations of individual molecules and even to control individual steps in a chemical reaction. Now we are developing new methods of changing the bonds themselves to form isomers that would normally not be so easy to swap.

Research like this not only helps make chemistry more precise, but also provides engineers with sharp new tools to build machines at the nanoscale, deforming carbon scaffolds into exotic shapes that would be impossible with conventional chemistry.

This study was published in The science.

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