A team of researchers from Hokkaido University, Japan, has isolated a compound in which a single electron is shared between two carbon atoms in what they have described as a “remarkably stable” covalent bond.
Covalent bonds – which see two atoms bound together by sharing a pair of electrons – are one of the fundamentals of chemistry and underpin the majority of organic compounds.
In 1931, the Nobel Prize-winning chemist Linus Pauling suggested that covalent bonds made from just a single, unpaired electron could exist, but these single-electron bonds would likely be much weaker.
While single-electron bonds have been observed, they haven’t been seen in carbon or hydrogen said Professor Yusuke Ishigaki, of the Department of Chemistry at Hokkaido University, who co-authored the study. He said that understanding the nature of single-electron sigma-bonds between two carbon atoms is essential to gain a deeper understanding of chemical-bonding theories - and could provide further insights into chemical reactions.
The single-electron bond was formed taking a derivative of hexaphenylethane - which contains an extremely stretched out paired-electron covalent bond between two carbon atoms - and subjecting it to an oxidation reaction in the presence of iodine. The reaction produced dark violet-colored crystals of an iodine salt.
The team used X-ray diffraction analysis to study the crystals and found that the carbon atoms in them were extremely close together, suggesting the presence of single-electron covalent bonds, something they then confirmed using Raman spectroscopy.
The results are the first piece of experimental evidence for a carbon-carbon single-electron covalent bond, which is likely to open the way for developments of the chemistry of this type of bonding, the researchers said. “The results of this paper unequivocally demonstrate the existence of a C-C one-electron σ-bond, which was postulated nearly a century ago,” said the paper, published in Nature.
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