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CAS numbers and nomenclature February 19, 2009

Posted by fetzthechemist in Uncategorized.

I have, repeatedly over the years, run into some misconceptions about Chemical Abstracts Service (CAS) numbers and nomenclature.

CAS is a literature service that abstracts and categorizes publications. It is staffed by a mix of information scientists (the librarian types) and scientists mainly from biology, chemistry, and physics). These are regular people doing jobs.

In nomenclature, they have people who have specialized at trying to understand and apply IUPAC rules. The are not infallable, though. They can get hierarchies wrong, using a rule on precidence incorrectly. They know more than most others because nomenclature is their job, but the CAS names are not chiselled in stone for correctness.

A CAS number are not just assigned to pure, known chemical. Mixtures get them, too. Things like gasoline, kerosene, and other commercial products get one. So does any process intermediate deemed important. In fact, a mixture can have more than one CAS number. Something like the petroleum distillate naphtha has at least a couple dozen CAS numbers.

One reason for this is that CAS numbers are not only assigned by CAS. They are also sold as part of the services. Any scientist or company can pay a fee to have a CAS number assigned to something that has not appeared in a published paper. Pre-patent materials and compounds are the biggest category here. A CAS number is needed or helpful in patent applications or some journals require a CAS number to be given in the manuscript, which is tough to do for a new compound.

If structures are complex, DAS numbers can be assigned or bought more than once, with different naming, too.



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