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This article is from the Chemistry
FAQ, by Bruce Hamilton B.Hamilton@irl.cri.nz with numerous
contributions by others.
12.1 What are CAS Registry Numbers? (Chemistry)
When chemicals are first encountered by the Chemical Abstracts Service, they
are assigned a unique number when they are registered. These numbers are not
related to any structure or property of the molecule, they are arbitrarily
assigned. It should be remembered that occasionally a compound may be
accidentally assigned two or more numbers - especially industrial products
that have not been completely characterised. When this is discovered, one of
the numbers is no longer used. The numbers usually take the form of
[xx-yy-z to xxxxxx-yy-z] and square brackets are often used in monographs to
identify the CAS Registry Number [RN]. The easiest way to locate the CAS RN
for commercially-available chemicals is to look in suppliers catalogues
( eg Aldrich) or compilations ( eg Merck or Hawley ), almost all chemical
texts now list the RN, and several ( eg Merck Index and Aldrich ) have a
cross-reference Index. The RN is extremely useful for on-line searching of
Chemical Abstracts and several other popular chemistry-related databases,
but is not particularly useful for the hardcopy version, except to confirm
compound identity.
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