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C and E News: Carbon atom chains observed June 4, 2009

Posted by fetzthechemist in Uncategorized.

The June 1st Chemical and Engineering News had a piece on page 7 about a group of Chinese researchers who used a transition electron microscope to cut a single chain of carbon atoms off ofd a graphene.

This is interesting in the advance in carbon materials. It caught my eye, however for two reasons. Two paragraphs of the article:

“The TEM resolution was not high enough to determine whether the chains were composed of cumulene, in which all carbons are connected by double bonds, or polyyne, which has carbons connected by alternating single and triple bonds.

The researchers found that the connection between the chains and the graphene was not stable, and a chain end would occasionally migrate along the edge of the graphene. Chains survived for as long as 100 seconds. When they broke, it was not in the middle. Instead, one end would detach and join its mate on the other edge of the graphene.”

First, the almost toss-off line about not determining whether this chain was really cumulative double bonds versus alternating triple bonds, cumulene versus polyacetylenic structure is not an easy experiment. The commonest techniques to differentiate are incompatible (NMR), not sensitive enough (Raman or IR), pr not valid for some reason. Both forms, however, ought to be somewhat linear chains. The electron arrangements could be very fluid between the two forms. Afterall, only electron movement might be happening.

The ending about one reactive end linking up to its mate resonates mentally with the apocryphal Kekule dream of a snake eating its own tail.



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