Chemistry: Ways to Search

CAS Registry Numbers

Chemical Abstracts Service has assigned a number to each chemical to simplify your search.

Each CAS Registry Number^® (CAS RN^®) identifier:

Is a unique numeric identifier
Designates only one substance
Has no chemical significance
Is a link to a wealth of information about a specific chemical substance

CAS registry numbers appear as three numbers separated by hyphens. For example, Francium: 7440-73-5

Look up RN numbers using:

ChemIDPlus Advanced
"Search and display of registry number, chemical name, molecular formula, structure, physical and toxicological properties plus locator and classification data."

ChemSpider

Chemical Structures

A variety of structure searching mechanisms are available in print indexes. Structure drawing tools are available for online resources.

Sigma-Aldrich Catalog: Search for a structure

ChemIDPlus Advanced: Search for a structure

ChemSpider Structure Search: Search engine provided by the Royal Society of Chemistry. Searches by name and RN number are also available.

Searching by Chemical Name

Nomenclature systems vary. Names can be complex, making searching prone to problems with typos, variant naming systems, etc. Most chemical reference works will have a name index. Review the material in the front of the book or on the help screens to understand which system they are using.

Try these resources to search by chemical names:

ChemID Plus Advanced will provide synonyms, CAS registry numbers, properties, and database links for various chemicals.

Search NIST Chemistry Web Book by chemical name.

Chemical naming Resources:

IUPAC Compendium of Chemical Terminology - the Gold Book

Periodic Table on the Web

Web Elements
Periodic table on the web

Chemical ID

ChemID Plus Advanced
"Search and display of registry number, chemical name, molecular formula, structure, physical and toxicological properties plus locator and classification data."