Covalent bonds, the very backbone of organic compounds, are formed when two atoms share a pair of electrons. Back in 1931, the renowned Linus Pauling proposed the existence of covalent bonds created from a single, unpaired electron. However, these single-electron bonds were expected to be considerably weaker than the standard two-electron covalent bonds.
Since then, single-electron bonds have been observed, but never before between carbon or hydrogen atoms. The pursuit of these one-electron bonds between carbon atoms has long perplexed scientists.
Now, a breakthrough has been achieved! A team of researchers from Hokkaido University has successfully isolated a compound where a single electron is shared between two carbon atoms, forming an exceptionally stable covalent bond known as a sigma bond.
“Elucidating the nature of single-electron sigma-bonds between two carbon atoms is essential to gain a deeper understanding of chemical-bonding theories and would provide further insights into chemical reactions,” explains Professor Yusuke Ishigaki of the Department of Chemistry at Hokkaido University, co-authored the study.
Through a series of groundbreaking experiments, researchers have achieved a remarkable feat: the creation of a single-electron bond. By subjecting a derivative of hexaphenylethane to an oxidation reaction in the presence of iodine, they produced striking dark violet-colored crystals of iodine salt.
Analysis using X-ray diffraction revealed an unprecedented closeness between the carbon atoms, hinting at the presence of single-electron covalent bonds. This groundbreaking discovery opens up new possibilities in the realm of chemical bonding and molecular structure.
“These results thus constitute the first piece of experimental evidence for a carbon-carbon single-electron covalent bond, which can be expected to pave the way for further developments of the chemistry of this scarcely-explored type of bonding,” says Takuya Shimajiri, the lead author of the paper and now at the University of Tokyo.
Journal reference:
- Takuya Shimajiri, Soki Kawaguchi, Takanori Suzuki & Yusuke Ishigaki. Direct evidence for a carbon–carbon one-electron σ-bond. Nature, 2024; DOI: 10.1038/s41586-024-07965-1
