The Chemical Abstracts Service
is part of the American Chemical Society
and maintains a database of chemical compounds and sequences. The CAS database currently contains over 55 million different organic and inorganic chemical compounds. Each CAS entry is identified by their CAS Registry Number, or CAS RN for short.
CAS Numbers themselves are up to 10 digits long using the format xxxxxxx-yy-z. They are assigned to a compound as the CAS registers a new compound. The number has no significance to the chemistry, structure or chemical nature of the molecule.
The CAS Number of a compound is a useful way to identify a chemical over its name. For example, the compound CAS 64-17-5 refers to ethanol. Ethanol is also known as ethyl alcohol, ethyl hydrate, absolute alcohol, grain alcohol, hydroxyethane. The CAS number is the same for all these names.
The CAS Number can also be used to distinguish between stereoisomers of a compound. Glucose is a sugar molecule that has two forms: D-glucose and L-glucose. D-glucose is also called dextrose and has CAS number 50-99-7. L-glucose is the mirror image of D-glucose and has a CAS Number of 921-60-8.