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Chemistry & Biochemistry: Chemical Searching

Need for Chemical Identifiers

Searching for and referring to chemicals is tricky because there are many names for each.

Salt for example, NaCl, is also known as sodium chloride, table salt, halite, saline, rock salt and many other synonyms. 

In an attempt to simplify matters, several schemes of chemical identifiers have been created. This is useful as it overcomes the limits of chemical naming systems, and can make searching for chemicals easier, especially across different languages.

CAS RN | Chemical Abstract Service Registry Number

Chemical Abstract Services (CAS), is a division on the American Chemical Society (ACS). They have a registry service that assigns strings of text to refer to chemical substances, thereby acting as a chemical identifier. They are up to 10 digits long and are separated into three groups by hyphens.

CAS numbers can be found in SciFinder, CAS publications, government sources, like PubMed and PubChem, some Elsevier databases, reference works and chemical catalogs.

Official CAS Registry and CAS Registry Number FAQs 


58-08-2 is C8H10N4O2 or caffeine

7697-37-2 is HNO3 or nitric acid

7647-14-5 is NaCl or sodium chloride

InChI | International Chemical Identifier

The International Union of Pure and Applied Chemistry (IUPAC), created the International Chemical Identifier (InChI), pronounced "inchy", to act as a barcode, so that data on a particular chemical and it’s structure, including all the different variants are included.

These strings have a hierarchical structure and represent the chemical structure – it has all the details and can handle tautomers (molecules with different forms). As a result these can get pretty long, so they can be shortened to an InChI Key.

InChI Trust YouTube channel explains the how the stings are formulated.


InChI=1S/C8H10N4O2/c1-10-4-9-6-5(10)7(13)12(3)8(14)11(6)2/h4H,1-3H3 is C8H10N4O2 or caffeine


InChI=1S/HNO3/c2-1(3)4/h(H,2,3,4) is HNO3 or nitric acid


InChI=1S/ClH.Na/h1H;/q;+1/p-1 is NaCl or sodium chloride



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Kristen Adams

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