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A CAS Registry Number (also referred to as CAS RN or informally CAS Number) is a
unique identification number assigned by the
Chemical Abstracts Service
CAS (formerly Chemical Abstracts Service) is a division of the American Chemical Society. It is a source of chemical information. CAS is located in Columbus, Ohio, United States.
Print periodicals
''Chemical Abstracts'' is a periodical index tha ...
(CAS), US to every
chemical substance
A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., wi ...
described in the open scientific literature. It includes all substances described from 1957 through the present, plus some substances from as far back as the early 1800s.
[ It is a ]chemical database
A chemical database is a database specifically designed to store chemical information. This information is about chemical and crystal structures, spectra, reactions and syntheses, and thermophysical data.
Types of chemical databases
Bioactivit ...
that includes organic and inorganic
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...
compounds, mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...
s, isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...
s, alloys
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, ...
, mixtures, and nonstructurable materials (UVCBs, substances of unknown or variable composition, complex reaction products, or biological origin). CAS RNs are generally serial number
A serial number is a unique identifier assigned incrementally or sequentially to an item, to ''uniquely'' identify it.
Serial numbers need not be strictly numerical. They may contain letters and other typographical symbols, or may consist enti ...
s (with a check digit
A check digit is a form of redundancy check used for error detection on identification numbers, such as bank account numbers, which are used in an application where they will at least sometimes be input manually. It is analogous to a binary parity ...
), so they do not contain any information about the structures themselves the way SMILES
The simplified molecular-input line-entry system (SMILES) is a specification in the form of a line notation for describing the structure of chemical species using short ASCII strings. SMILES strings can be imported by most molecule editors f ...
and InChI
The International Chemical Identifier (InChI or ) is a textual identifier for chemical substances, designed to provide a standard way to encode molecular information and to facilitate the search for such information in databases and on the we ...
strings do.
The registry maintained by CAS is an authoritative collection of disclosed chemical substance information. It identifies more than 182 million unique organic and inorganic substances and 68 million protein and DNA sequences, plus additional information about each substance. It is updated with around 15,000 additional new substances daily. A collection of almost 500 thousand CAS registry numbers are made available under a CC-BY-NC
A Creative Commons NonCommercial license (CC NC, CC BY-NC or NC license) is a Creative Commons license which a copyright holder can apply to their media to give public permission for anyone to reuse that media only for noncommercial activities. C ...
license at ACS Commons Chemistry.
Use
Historically, chemicals have been identified by a wide variety of synonyms. Frequently these are arcane and constructed according to regional naming conventions relating to chemical formulae, structures or origins. Well-known chemicals may additionally be known via multiple generic, historical, commercial, and/or (black)-market names.
CAS Registry Numbers (CAS RN) are simple and regular, convenient for database searches. They offer a reliable, common and international link to every specific substance across the various nomenclatures and disciplines used by branches of science, industry, and regulatory bodies. Almost all molecule databases today allow searching by CAS Registry Number.
Format
A CAS Registry Number has no inherent meaning, but is assigned in sequential, increasing order when the substance is identified by CAS scientists for inclusion in the CAS REGISTRY database.
A CAS RN is separated by hyphens into three parts, the first consisting from two up to seven digits, the second consisting of two digits, and the third consisting of a single digit serving as a check digit
A check digit is a form of redundancy check used for error detection on identification numbers, such as bank account numbers, which are used in an application where they will at least sometimes be input manually. It is analogous to a binary parity ...
. This format gives CAS a maximum capacity of 1,000,000,000 unique numbers.
The check digit is found by taking the last digit times 1, the preceding digit times 2, the preceding digit times 3 etc., adding all these up and computing the sum modulo 10. For example, the CAS number of water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
is 7732-18-5: the checksum 5 is calculated as (8×1 + 1×2 + 2×3 + 3×4 + 7×5 + 7×6) = 105; 105 mod 10 = 5.
Granularity
* Stereoisomer
In stereochemistry, stereoisomerism, or spatial isomerism, is a form of isomerism in which molecules have the same molecular formula and sequence of bonded atoms (constitution), but differ in the three-dimensional orientations of their atoms in ...
s and racemic mixture
In chemistry, a racemic mixture, or racemate (), is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule or salt. Racemic mixtures are rare in nature, but many compounds are produced industrially as racemates. ...
s are assigned discrete CAS Registry Numbers: L-epinephrine
Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands and ...
has 51-43-4, D-epinephrine has 150-05-0, and racemic DL-epinephrine has 329-65-7
* Different phase
Phase or phases may refer to:
Science
*State of matter, or phase, one of the distinct forms in which matter can exist
*Phase (matter), a region of space throughout which all physical properties are essentially uniform
* Phase space, a mathematic ...
s do not receive different CAS RNs (liquid water and ice both have 7732-18-5), but different crystal structures do (carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
in general is 7440-44-0, graphite
Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on large ...
is 7782-42-5 and diamond
Diamond is a Allotropes of carbon, solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the Chemical stability, chemically stable form of car ...
is 7782-40-3)
* Commonly encountered mixtures of known or unknown composition may receive a CAS RN; examples are Leishman stain
Leishman stain, also known as Leishman's stain, is used in microscopy for staining blood smears. It is generally used to differentiate between and identify white blood cells, malaria parasites, and trypanosomas. It is based on a methanolic mixture ...
(12627-53-1) and mustard oil
Mustard oil can mean either the pressed oil used for cooking, or a pungent essential oil also known as volatile oil of mustard. The essential oil results from grinding mustard seed, mixing the grounds with water, and extracting the resulting vol ...
(8007-40-7).
* Some metals are discerned by their oxidation state, e.g. the element chromium
Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal.
Chromium metal is valued for its high corrosion resistance and hardne ...
has 7440-47-3, the trivalent Cr(III) has 16065-83-1 and the hexavalent Cr(VI) ion has 18540-29-9.
* Occasionally whole classes of molecules receive a single CAS RN: the class of enzymes known as alcohol dehydrogenase
Alcohol dehydrogenases (ADH) () are a group of dehydrogenase enzymes that occur in many organisms and facilitate the interconversion between alcohols and aldehydes or ketones with the reduction of nicotinamide adenine dinucleotide (NAD+) to N ...
s has 9031-72-5.
Search engines
* CHEMINDEX Search via Canadian Centre for Occupational Health and Safety
The Canadian Centre for Occupational Health and Safety (CCOHS) is an independent departmental corporation under Schedule II of the Financial Administration Act and is accountable to Parliament through the Minister of Labour.
CCOHS functions as the ...
* ChemIDplus Advanced via United States National Library of Medicine
The United States National Library of Medicine (NLM), operated by the United States federal government, is the world's largest medical library.
Located in Bethesda, Maryland, the NLM is an institute within the National Institutes of Health. Its ...
* Common Chemistry via Australian Inventory of Chemical Substances
* European chemical Substances Information System
The European chemical Substances Information System (ESIS) was a chemoinformatics database that stored information system on chemicals of the European Union. It was created by the former European Chemicals Bureau, which completed its mandate in 20 ...
via the website of Royal Society of Chemistry
The Royal Society of Chemistry (RSC) is a learned society (professional association) in the United Kingdom with the goal of "advancing the chemistry, chemical sciences". It was formed in 1980 from the amalgamation of the Chemical Society, the Ro ...
* HSNO Chemical Classification Information Database via Environmental Risk Management Authority
* Search Tool of Australian Inventory of Chemical Substances
*USEPA CompTox Chemicals Dashboard
See also
* Academic publishing
Academic publishing is the subfield of publishing which distributes academic research and scholarship. Most academic work is published in academic journal articles, books or theses. The part of academic written output that is not formally publ ...
* Beilstein Registry Number The Beilstein Registry Number is a way of identifying compounds similar to the CAS registry number. It is the unique identifier
A unique identifier (UID) is an identifier that is guaranteed to be unique among all identifiers used for those objec ...
* Chemical file format
A chemical file format is a type of data file which is used specifically to depicting molecular data. One of the most widely used is the chemical table file format, which is similar to ''Structure Data Format'' (SDF) files. They are text files ...
* Dictionary of chemical formulas
This is a list of common chemical compounds with chemical formulae and CAS numbers, indexed by formula.This complements alternative listing at list of inorganic compounds. There is no complete list of chemical compounds since by nature the list ...
* EC# (EINECS and ELINCS, European Community)
* EC number (Enzyme Commission)
* International Union of Pure and Applied Chemistry
The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
* List of CAS numbers by chemical compound
This is a list of CAS numbers by chemical formulas and chemical compounds, indexed by formula.The CAS number is a unique number applied to a specific chemical by the Chemical Abstracts Service (CAS).This list complements alternative listings to be ...
* MDL number
* PubChem
PubChem is a database of chemical molecules and their activities against biological assays. The system is maintained by the National Center for Biotechnology Information (NCBI), a component of the National Library of Medicine, which is part of ...
* Registration authority
Registration authorities exist for many standards organizations, such as ANNA (Association of National Numbering Agencies for ISIN), the Object Management Group, W3C, IEEE and others. In general, registration authorities all perform a similar fun ...
* UN number
A UN number (United Nations number) is a four-digit number that identifies hazardous materials, and articles (such as explosives, flammable liquids, oxidizers, toxic liquids, etc.) in the framework of international trade and transport. Some hazard ...
Notes
External links
CAS registry description
by Chemical Abstracts Service
To find the CAS number of a compound given its name, formula
In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwee ...
or structure, the following free resources can be used:
NLM,NIH ChemIDplus
NIST Chemistry WebBook
NCI/CADD Chemical Identifier Resolver
ChemSub Online (Multilingual chemical names)
{{DEFAULTSORT:Cas Registry Number
Chemical numbering schemes
American Chemical Society
Unique identifiers