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CAS registry numberCAS registry numbers are unique numerical identifiers for chemical compounds, polymers, biological sequences, mixtures and alloys. They are also referred to as CAS numbers, CAS RNs or CAS #s. Chemical Abstracts Service (CAS), a division of the American Chemical Society, assigns these identifiers to every chemical that has been described in the literature. The intention is to make database searches more convenient, as chemicals often have many names. Almost all molecule databases today allow searching by CAS number. As of October 2007, there were 32,813,596 organic and inorganic substances and 59,404,558 sequences in the CAS registry.^{[1]} Around 50,000 new numbers are added each week. CAS also maintains and sells a database of these chemicals, known as the CAS registry.
FormatA CAS registry number is separated by hyphens into three parts, the first consisting of up to 7 digits, the second consisting of two digits, and the third consisting of a single digit serving as a check digit. The numbers are assigned in increasing order and do not have any inherent meaning. The checksum is calculated by taking the last digit times 1, the next digit times 2, the next digit times 3 etc., adding all these up and computing the sum modulo 10. For example, the CAS number of water is 7732185: the checksum is calculated as (8×1 + 1×2 + 2×3 + 3×4 + 7×5 + 7×6) = 105; 105 mod 10 = 5. The Chemical Abstracts Service has announced on its web site that it will add an additional digit to new CAS registry numbers, starting about January 2008. Isomers, enzymes, and mixturesDifferent stereoisomers of a molecule receive different CAS numbers: Dglucose has 50997, Lglucose has 921608, αDglucose has 26655345, etc. Occasionally, whole classes of molecules receive a single CAS number: the group of alcohol dehydrogenases has 9031725. An example of a mixture with a CAS number is mustard oil (8007407). SearchesWhen using CAS numbers for database searches, it is useful to include the numbers of closely related compounds. For instance, to search for information about cocaine (CAS 50362), one should consider including cocaine hydrochloride (CAS 53214), since that is the most common form of cocaine when used as a drug. Notes
See also
To find the CAS number of a compound given its name, formula or structure, the following free resources can be used:
Categories: Chemical numbering schemes  American Chemical Society 

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "CAS_registry_number". A list of authors is available in Wikipedia. 