CAS registry numbers are unique numerical identifiers for chemical compounds, polymers, biological sequences, mixtures and alloys. A chemical compound is a substance consisting of two or more different elements chemically bonded together in a fixed proportion by Mass. A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds An alloy is a Solid solution or Homogeneous mixture of two or more elements, at least one of which is a Metal, which itself has 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. Chemical Abstracts Service ( CAS) is a division of the American Chemical Society, and produces Chemical Abstracts, and related products The American Chemical Society ( ACS) is a Learned society ( Professional association) based in the United States that supports scientific inquiry 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 January 2008, there were 33,565,050 organic and inorganic substances and 59,584,048 sequences in the CAS registry. PortalCurrent events International holidays January 1 - New Year's Day January 1 - Independence  Around 50,000 new numbers are added each week.
CAS also maintains and sells a database of these chemicals, known as the CAS registry.
A 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. A check digit is a form of Redundancy check used for Error detection, the decimal equivalent of a binary Checksum. 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. In Mathematics, modular arithmetic (sometimes called modulo arithmetic, or clock arithmetic) is a system of Arithmetic for Integers For example, the CAS number of water is 7732-18-5: the checksum is calculated as (8×1 + 1×2 + 2×3 + 3×4 + 7×5 + 7×6) = 105; 105 mod 10 = 5. Water is a common Chemical substance that is essential for the survival of all known forms of Life.
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.
Different stereoisomers of a molecule receive different CAS numbers: D-glucose has 50-99-7, L-glucose has 921-60-8, α-D-glucose has 26655-34-5, etc. Stereoisomers are isomeric molecules that have the same molecular formula and sequence of bonded atoms (constitution but which differ in the three dimensional orientations Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. Occasionally, whole classes of molecules receive a single CAS number: the group of alcohol dehydrogenases has 9031-72-5. Alcohol dehydrogenase (ADH is an enzyme discovered in the mid-1960s in Drosophila melanogaster. An example of a mixture with a CAS number is mustard oil (8007-40-7). The term mustard oil is used for two different oils that are made from Mustard seeds a fatty Vegetable oil resulting from pressing the seeds
When 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 50-36-2), one should consider including cocaine hydrochloride (CAS 53-21-4), since that is the most common form of cocaine when used as a drug. Cocaine ( benzoylmethyl ecgonine) is a Crystalline Tropane Alkaloid that is obtained from the leaves of the Coca plant In chemistry hydrochlorides are salts resulting or regarded as resulting from the reaction of Hydrochloric acid with an organic base (mostly Amines
To find the CAS number of a compound given its name, formula or structure, the following free resources can be used: