The identification of a stable single-electron covalent bond between two carbon atoms supports a theory that has been around for a century.
The identification of a stable single-electron covalent bond between two carbon atoms supports a theory that has been around for a century.
Covalent bonds, which involve the sharing of a pair of electrons between two atoms, form the foundation for most organic compounds. In 1931, Nobel Prize winner Linus Pauling proposed the idea that covalent bonds could exist with just one unpaired electron; however, he noted that these single-electron bonds would probably be less robust than traditional covalent bonds that involve two electrons.
Although single-electron bonds have been discovered in other contexts, they had not been found in carbon or hydrogen, making the search for one-electron bonds between carbon atoms a significant challenge for scientists.
Recently, researchers from Hokkaido University successfully isolated a compound in which a single electron is shared between two carbon atoms, forming a notably stable covalent bond known as a sigma bond. Their research appears in the journal Nature.
“Understanding the characteristics of single-electron sigma bonds between carbon atoms is crucial for enhancing our knowledge of chemical-bonding theories and will offer additional insights into chemical reactions,” said Professor Yusuke Ishigaki from Hokkaido University’s Department of Chemistry, who contributed to the research.
The single-electron bond was created by oxidizing a derivative of hexaphenylethane, which already has a significantly extended paired-electron covalent bond between two carbon atoms, in the presence of iodine. This chemical reaction yielded dark violet crystals of an iodine salt.
The research team utilized X-ray diffraction analysis to examine the crystals and discovered that the carbon atoms were remarkably close to one another, indicating the existence of single-electron covalent bonds. They confirmed this finding through a chemical analysis technique known as Raman spectroscopy.
“These findings represent the first experimental evidence of a carbon-carbon single-electron covalent bond, potentially opening the door to further exploration in this less-studied area of chemistry,” stated Takuya Shimajiri, the primary author of the study, who is currently associated with the University of Tokyo.
