Have a look at the structure (a).
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| (a) |
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Applying von Baeyer nomenclature, we get a horrendously long and unwieldy name ‘pentacyclo[19.3.1.13,7.19,13.115,19]octacosa-1(25),3(28),4,6,9(27),10,12,15(26),16,18,21,23-dodecaene’. I think it’s a crime to name a beautifully symmetrical structure like (a) in such a fashion. Can’t we create a name that states the obvious: (a) is a big cycle containing four benzene rings?
After hours spent looking in my books and searching the internet, I came to the conclusion that chemists talk about chains and rings without explaining what they mean. The only definition I found so far, viz. that of Gold Book, is specific for polymers and seems to be too complex to be used in general chemical nomenclature:
The whole or part of a macromolecule, an oligomer molecule or a block, comprising a linear or branched sequence of constitutional units between two boundary constitutional units, each of which may be either an end-group, a branch point or an otherwise-designated characteristic feature of the macromolecule. |
(1) |
On the other hand, general dictionary definitions of (chemical) chains are not precise enough. For example, Collins English Dictionary defines chain (chemistry) as
two or more atoms or groups bonded together so that the configuration of the resulting molecule, ion, or radical resembles a chain. |
(2) |
whereas Merriam-Webster says that it is
a number of atoms or chemical groups united like links in a chain. |
(3) |
So chain (chemistry) is like a chain. Is it?
To date, two types of enzymes that are responsible for primary attack of polyisoprene in rubber-degrading microorganisms have been identified [1]. One is the latex clearing protein (Lcp), first isolated from Streptomyces sp., which does not have any metal ions or cofactors [2]. The other is the rubber oxygenase RoxA of Xanthomonas sp., a dihaem c-type cytochrome that cleaves cis-1,4-polyisoprene, the main constituent of natural rubber, to 12-oxo-4,8-dimethyltrideca-4,8-diene-1-al [3, 4]. The crystal structure of RoxA, solved at 1.8 Å resolution, was released today [5].
The recent Nature publication shows that one can literally see a mechanically-induced ring-opening reaction.
 | Previously, we have shown with dissolved polymer strands incorporating mechanically sensitive chemical groups — so-called mechanophores — that the directional nature of mechanical forces can selectively break and re-form covalent bonds. We now demonstrate that such force-induced covalent-bond activation can also be realized with mechanophore-linked elastomeric and glassy polymers, by using a mechanophore that changes colour as it undergoes a reversible electrocyclic ring-opening reaction under tensile stress and thus allows us to directly and locally visualize the mechanochemical reaction. We find that pronounced changes in colour and fluorescence emerge with the accumulation of plastic deformation, indicating that in these polymeric materials the transduction of mechanical force into the ring-opening reaction is an activated process. |
I guess we have to introduce a new ChEBI role: mechanophore.
