June 27, 2001 -- Life is based on carbon, and bonds between carbon atoms are found in all living organisms. Students in organic and biochemistry are taught that the longest common carbon bond is found in diamond, a form of pure carbon. But now, Utah chemists have discovered a new type of carbon-carbon bond that is almost twice as long.

“This is a big jump, but if you have no interest in chemistry, it’s not going to make your life different,” said Joel Miller, a distinguished professor of chemistry at the University of Utah. “Gee whiz is one way of looking at it. These are substantially longer carbon-carbon bonds than ever observed before. This is very surprising.”

While potential applications of such basic research are difficult to predict, Miller said the new kind of carbon bond may be important in efforts to develop nanomaterials,” which are bigger than typical molecules but smaller than the smallest manufactured parts and are being studied for possible use in faster computers, display devices and micromachines.

The new, long type of bond between carbon atoms is not found in living organisms or diamond. Instead, Miller discovered it in organic chemicals named TCNE, TCNQ and DDQ.

Atomic distances and bonds are measured in units known as angstroms. An angstrom is equal to one ten-billionth of a meter. (A meter is almost 39.4 inches). A sheet of paper is about 1 million angstroms thick.

For decades, students in biochemistry and organic chemistry have been taught that the longest common bond between two carbon atoms is found in diamond and measures 1.54 angstroms. In some cases, chemists have made carbon bonds as long as 1.73 angstroms by attaching bulky components to molecules to stretch the carbon-carbon bonds, Miller said.

In the organic chemicals Miller studied, the bond between two carbon atoms ranged from 2.83 to 3.09 angstroms long – almost twice the length of the carbon-carbon bonds in diamond, he said.

Miller and University of Utah chemistry doctoral student Rico E. Del Sesto published the discovery June 27 in the online edition of a widely cited English-language German chemistry journal, Angewandte Chemie (Applied Chemistry). It will appear soon in the printed edition. The study was co-authored by chemists Juan J. Novoa and Pilar Lafuente of the University of Barcelona in Spain. Miller said the Spanish chemists described the long carbon-carbon bonding in mathematical terms needed for the paper.

“Carbon-carbon bonding is the essential ingredient to life and to all organic and biochemistry, and is perhaps the best studied of all chemical bonds,” Miller said. “As a consequence, new information about carbon-carbon bonding is important. People always think of carbon-carbon bonds as never exceeding 1.54 angstroms, and essentially we are doubling it.”

Miller’s research deals largely with organic molecules, such as TCNE (tetracyanoethylene), that have magnetic properties and thus have been nicknamed “plastic magnets.” He essentially stumbled on the long carbon bonds doing such work.

The chemists found nine different examples of the long type of carbon-carbon bonds. Two negatively charged ions of TCNE, forced together by surrounding positive charges, bond together with the new, long carbon-carbon bond to form a bigger more negatively charged ion. In a typical carbon bond, two carbon atoms share two electrons, but in this case, the bond involves four carbon atoms sharing two electrons, Miller said.

If carbon bonds are ubiquitous, why were long carbon bonds discovered only now?

“They are only found in a small class of special compounds,” Miller said.

The chemical structure of the compounds and the distances between their carbon atoms were known previously, “but they were not appreciated as a genuine carbon-carbon bond,” he added.

There are different kinds of chemical bonds, and the precise definition of chemical bonding at times “is a difficult question for a chemist, let alone non-chemists,” Miller said.

But the newly discovered carbon-carbon bond meets accepted definitions, he added.

Miller said the new type of bond is stable but weak – which means it breaks more easily than bonds in which carbon atoms are closer to each other – and it is conceivable that some chemists might argue it is not a true bond. But researchers who reviewed the study for the journal raised no such objections, he added.

Miller’s web sites are:
http://www.chem.utah.edu/chemistry/faculty/miller/miller.html
http://www.chem.utah.edu/chemistry/faculty/miller/millergroup/main.html