Editing CAS Registry Number (section)

{{Short description|Chemical identifier}}
{{Use dmy dates|date=May 2018}}
[[File:Cascommonchemistry2022.png|thumb|Screenshot of the CAS Common Chemistry database with information about [[caffeine]] ([https://commonchemistry.cas.org/detail?cas_rn=58-08-2 58-08-2]).]]
 
A '''CAS Registry Number'''<ref>[http://www.cas.org/expertise/cascontent/registry/regsys.html CAS registry description] {{Webarchive |url=https://web.archive.org/web/20080725010848/http://www.cas.org/expertise/cascontent/registry/regsys.html# |date=2008-07-25 }}, by Chemical Abstracts Service</ref> (also referred to as '''CAS RN'''<ref>{{cite web|url=https://www.cas.org/support/documentation/chemical-substances/cas-rn-verified-partner-program|title=CAS Registry Number Verified Partner Program|access-date=2021-08-04|publisher=CAS}}</ref> or informally '''CAS Number''') is a [[unique identifier|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.<ref name=CAScontent/> It is a [[chemical database]] that includes [[Organic compounds|organic]] and [[inorganic compounds|inorganic]] compounds, [[mineral]]s, [[isotope]]s, [[alloys]], mixtures, and nonstructurable materials (UVCBs - substances of '''u'''nknown or '''v'''ariable composition, '''c'''omplex reaction products, or '''b'''iological origin).<ref name=crc>{{cite web |author=American Chemical Society |author-link=American Chemical Society |title=CAS Registry and CASRNs |url=http://www.cas.org/expertise/cascontent/registry/regsys.html#q2 |access-date=2009-07-25 |archive-url=https://web.archive.org/web/20080725010848/http://www.cas.org/expertise/cascontent/registry/regsys.html#q2#q2 |archive-date=2008-07-25 |url-status=dead |df=dmy-all}}</ref> CAS RNs are generally [[serial number]]s (with a [[check digit]]), so they do not contain any information about the structures themselves the way [[Simplified molecular-input line-entry system|SMILES]] and [[International Chemical Identifier|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,<ref name=CAScontent>{{cite web |title=CAS Content: Substances |url=https://www.cas.org/about/cas-content |website=www.cas.org|access-date=2020-08-10 |language=en}}</ref> plus additional information about each substance. It is updated with around 15,000 additional new substances daily.<ref>{{Cite web|url=https://www.cas.org/cas-data/cas-registry|title=CAS REGISTRY|website=www.cas.org}}</ref> A collection of almost 500 thousand CAS registry numbers is made available under a [[CC BY-NC]] license at ACS Commons Chemistry.<ref>{{cite news |title=CAS Common Chemistry expands collection of publicly available chemical information |url=https://www.cas.org/resources/press-releases/common-chemistry |access-date=17 March 2021 |work=CAS |language=en}}</ref>