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Carbon can exceed four-bond limit

Carbon can exceed four-bond limit

Chemists confirm links to six other atoms in unusual molecule

By
2:38pm, January 4, 2017
hexamethylbenzene

BONDING TIME  When hexamethylbenzene loses two electrons, it rearranges from a flat hexagonal ring into the five-sided pyramid shown here. The carbon atom on top of the pyramid bonds to six other carbon atoms as opposed to the usual four.

A molecule originally proposed more than 40 years ago breaks the rules about how carbon connects to other atoms, scientists have confirmed. In this unusual instance, a carbon atom bonds to six other carbon atoms. That structure, mapped for the first time using X-rays, is an exception to carbon’s textbook four-friend limit, researchers report in the Jan. 2 Angewandte Chemie.

Although the idea for the structure isn’t new, “I think it has a larger impact when someone can see a picture of the molecule,” says Dean Tantillo, a chemist at the University of California, Davis who wasn’t part of the study. “It’s super important that people realize that although we’re taught carbon can only have four friends, carbon can be associated with more than four atoms.”

Atoms bond by sharing

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