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CAS Registry Number

Screenshot of the CAS Common Chemistry database with information about caffeine (58-08-2).

A CAS Registry Number[1] (also referred to as CAS RN[2] or informally CAS Number) is a unique identification number, assigned by the Chemical Abstracts Service (CAS) in the US to every chemical substance described in the open scientific literature, in order to index the substance in the CAS Registry. This registry includes all substances described since 1957, plus some substances from as far back as the early 1800s;[3] it is a chemical database that includes organic and inorganic compounds, minerals, isotopes, alloys, mixtures, and nonstructurable materials (UVCBs, substances of unknown or variable composition, complex reaction products, or biological origin).[4] CAS RNs are generally serial numbers (with a check digit), so they do not contain any information about the structures themselves the way SMILES and InChI strings do.

The CAS Registry is an authoritative collection of disclosed chemical substance information. It identifies more than 204 million unique organic and inorganic substances and 69 million protein and DNA sequences,[3] plus additional information about each substance. It is updated with around 15,000 additional new substances daily.[5] A collection of almost 500 thousand CAS registry numbers are made available under a CC BY-NC license at ACS Commons Chemistry.[6]

  1. ^ CAS registry description Archived 2008-07-25 at the Wayback Machine, by Chemical Abstracts Service
  2. ^ "CAS Registry Number Verified Partner Program". CAS. Retrieved 4 August 2021.
  3. ^ a b "CAS Content: Substances". www.cas.org. Retrieved 10 August 2020.
  4. ^ American Chemical Society. "CAS Registry and CASRNs". Archived from the original on 25 July 2008. Retrieved 25 July 2009.
  5. ^ Chemical Substances – CAS REGISTRY
  6. ^ "CAS Common Chemistry expands collection of publicly available chemical information". CAS. Retrieved 17 March 2021.