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Toxics Cleanup Program Home > CLARC > CAS Registry Numbers and Chemical Names
CAS Registry Numbers and Chemical Names

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Chemical Abstracts Service (CAS) Registry Numbers

Every chemical can have many different names and if chemical information is not catalogued under the name one is using to search, information can be missed. Chemicals are assigned unique identifying numbers, Chemical Abstracts Service (CAS) Registry numbers, when they first appear in the chemical literature. Identification of a chemical by its CAS number reduces the difficulties that can occur when one attempts to locate information using a chemical name.

CLARC contains 19 substances that have not been assigned CAS numbers. These have been assigned identifiers of the form “unidentifiedxx” where xx is a two digit number:

Lead alkyls unidentified02
Monochlorobutanes unidentified03
Nickel refinery dust unidentified04
PAH unidentified05
Refractory ceramic fibers unidentified07
TPH: gasoline range organics, no detectable benzene unidentified08
TPH, diesel range organics unidentified09
TPH, heavy oils unidentified10
TPH, mineral oil unidentified11
Uranium, soluble salts unidentified12
Trihalomethanes, total (TTHMs) unidentified13
Sulfate unidentified17
Total dissolved solids unidentified18
pH unidentified19
gross alpha particle activity unidentified20
gross beta particle activity unidentified21
radium 226 and 228 unidentified23
radium 226 unidentified24
TPH: gasoline range organics, benzene present unidentified25

Chemical Names in CLARC

Names of organic chemicals are frequently preceded by numbers or certain letters used to describe the structure of the chemical. For the purpose of indexing chemical names in CLARC, this structural information is placed at the end of the chemical name. For example:

Chemical Name Chemical Name in CLARC
N,N-dimethylaniline dimethylaniline;N,N-
p-chlorophenol chlorophenol;p-
1,2-dichloroethane dichloroethane;1,2-
cis-1,2-dichloroethene dichloroethene;1,2-cis

For chemical names which have the prefix “bis,” the “bis” remains at the beginning in CLARC.