Subject: CAS Registry Numbers

From: Doug Smith <[email-masked]>
Date: Fri, 18 May 2001 10:15:34 -0400

Can someone explain the structure of a CAS registry number and how it is
generated?  According to the CAS web site, 336607-92-2 is the most recent
CAS Registry Number as of this morning.  I know there is no chemical meaning
or significance to the numbers, but what is each of the three fields and how
are the numbers assigned?
Doug

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From: Jonathan Brecher <[email-masked]>
Date: Fri, 18 May 2001 14:06:00 -0400

>are the numbers assigned?

See http://www.cas.org/EO/regsys.html

Briefly:

o  The last digit is a checksum.
o  Everything up to the last digit represents a sequential number.  The
number above corresponds to the 33,660,792th item entered into their
database. (Approximately!  The numbers didn't quite start at 1, and just
because it was the 33.6 millionth item entered, that doesn't mean that all
of the other items are still present in the database.  Numbers are retired,
etc...)
o  The dashes are there just to make things look pretty.

Jonathan Brecher
CambridgeSoft Corporation
[email-masked]

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From: William T Winter <[email-masked]>
Date: Fri, 18 May 2001 15:05:41 -0400

The following is taken from an paper by Robert E. Buntrock, a specialist in
chemical information, entitled "Chemical Registries - in the fourth Decade of
Service" and presented at the 218th ACS National Meeting in 1999... The complete
address may be read at http://www.lib.uchicago.edu/cinf/218nm/218acs41.htm
and is part of the ACS Division of Chemical Information pages

"...The format of CAS Registry Numbers is intentionally unique. As mentioned
previously, the number is a serial number; the next available
number is assigned to the next new compound to be entered into the file. (As an
aside, Registry Numbers have disappeared from the file. For
example, formaldehyde – CASRN 50-00-0, or compound number "5000" -- is serially
the second compound in the file.) The last number is an
algorithmically assigned check character. The format is from two to six numerals
followed by a hyphen, followed by two numerals, followed
by a hyphen, and concluding with one numeral. As indicated, 50-00-0,
formaldehyde, is compound 5000, and 1746-01-6, dioxin, is
compound 174,601. ..."

Doug Smith wrote:

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