Chemists discovered the first new chemical bond in more than a decade

Though it was first predicted in the 1930s, chemists have just now managed to create a covalent bond that only uses one electron

By Karmela Padavic-Callaghan

25 September 2024

Covalent bonds can contain two, four, six or eight electrons – or just one

SimoneN/Shutterstock

It is not often that chemists create a new kind of chemical bond, but they have just done it. A covalent bond that relies on a single electron has been made almost a century after it was first proposed.

Takuya Shimajiri at the University of Tokyo and his colleagues have been testing the limits of chemical bonds for years. Previously, they experimented with unusually long and flexible bonds, and now they have taken on an idea first proposed in 1931 by chemist Linus Pauling: a chemical bond formed by just one electron.

All known covalent bonds, where atoms connect by sharing electrons, contain two, four, six or eight electrons – but Pauling theorised a covalent bond could exist with a single electron shared between two atoms. To create this, the researchers used a chemical reaction to remove an electron from an existing two-electron covalent bond between two carbon atoms. They used a large hydrocarbon that has exceptionally long bonds between its carbon atoms, which means it would be energetically costly for an electron from elsewhere in the molecule to replace the one they removed.

Advertisement

Shimajiri says past experiments that attempted such electron subtraction left behind weak bonds which broke too quickly for a definitive chemical analysis. But his team’s molecule remained stable enough they could analyse it with X-rays and several kinds of light. Based on how this radiation bounced off or was absorbed, they determined it had a stable one-electron bond.

“It’s not often that you find a molecule with a new kind of bond,” says Henry Rzepa at Imperial College London. He says the molecule had a total of 278 electrons, so it was a real feat to both remove the correct one and prevent all the others from immediately replacing it. Rzepa says this is a “major discovery” that could lead chemists to create whole new families of molecules.

Can we solve quantum theory’s biggest problem by redefining reality?

With its particles in two places at once, quantum theory strains our common sense notions of how the universe should work. But one group of physicists says we can get reality back if we just redefine its foundations