Finding and Verifying CAS Registry Numbers^® on STN^®
— March 1993 —

The Registry File

Each REGISTRY File record contains information about a unique chemical substance, including the CAS Registry Number, chemical names, the molecular formula, and the chemical structure. The information in each record is searchable online.

Indexes in the REGISTRY File

The chemical information from the records is placed in searchable indexes. Each index consists of a list of words arranged in alphabetical order or numbers arranged in numeric order. These indexes are also known as “search fields.” In this booklet we will mention a few indexes of interest to your needs.

REGISTRY File access points
Registry Number Index	Chemical Name Index	Molecular Formula Index	Structures	Basic Index	Ring Data Index

Registry Number Index

It contains a list of CAS Registry Numbers for all types of substances, i.e., biochemical, organic, inorganic, metals, alloys, and polymers.

Chemical Name Index

Although there is only one Registry Number for a given substance, there can be anywhere from one to hundreds of names for a chemical. The types of names for a substance can include: the CA Index Name, IUPAC names, systematic names, semi-systematic names, trade names, and commonly used names. The CA Index Name is the “official” name that Chemical Abstracts Service assigns to a substance according to highly structured naming conventions (nomenclature). Many of the names CAS encounters as it abstracts and indexes the world’s chemical literature are placed in REGISTRY File records and the Chemical Name Index.

Molecular Formula Index

A molecular formula is another piece of identifying information for a chemical substance. But, a molecular formula is not unique for a substance. Many substances in the file have the same formula! For example, the molecular formula, C4H8, is used for Cyclobutane (Registry Number 287-23-0), as well as for l-butene (Registry Number 106-98-9). Thus, by itself, a formula is not enough information for easily finding a Registry Number.

Structures

A chemical structure is a diagram showing the arrangement of a substance’s elements and bonds. A structure diagram is unique to each substance, like a fingerprint is unique for a person. The structure of a substance is in a special index in the REGISTRY File. Searching by structure diagrams is beyond the scope of this introductory booklet. For more information on learning structure searching techniques, contact the STN Workshop coordinator at 1-800-848-6538.

Basic Index

The Basic Index is the primary index containing fragments (or portions) of chemical names. You can search name fragments in the Basic Index, including natural fragments, smallest fragments, and recombined fragments. For example, the name “2,4,6-trimethlybenzoic acid” would be divided into the following fragments:

The above fragments are in the Basic Index as separate search terms.

The Basic Index also contains molecular formulas for single component substances and for the individual components of multicomponent substances.

NOTE: Combining name fragment searching in the Basic Index with molecular formula searching in the Molecular Formula index is an effective method for finding a unique chemical substance in the REGISTRY File. Name fragment searching requires a good understanding of chemical nomenclature. Thus, this search method is beyond the scope of this introductory booklet.

Sample Record

These indexes are just a few of the many available for a substance record. In the REGISTRY File, the fields or indexes you can SEARCH are called “search fields.” The fields in a record that you can look at are called “display fields;” these are listed in Appendix 9 — Display Fields. Usually the search fields have corresponding display fields.

Each display field is identified by a code. The fields you will focus on include:

• RN = Registry Number
• CN = Chemical Names — the CA Index Name, followed by a list of the names for a substance that appear in chemical lists and literature.
• MF = Molecular Formula
• LC = Registry Number Locator — the names of other STN files and regulatory lists that contain information on this substance.

Here is a sample REGISTRY File record:

RN   40034-42-2 REGISTRY
CN   3-Quinolinecarboxylic acid, 1-ethyl-1,4-dihydro-4-oxo-7-(4-
       pyridinyl)- (9CI)  (CA INDEX NAME)

OTHER NAMES:
 CN   Acrosoxacin
 CN   Rosoxacin 
 FS   3D CONCORD
 MF   C17 H14 N2 03
 CI   COM
 LS   ANABSTR, BEILSTEIN, BIOSIS, CA, CIN, CJACS, EINECS, EMBASE,
        IFICDB,IFIPAT, IFIUDB, MEDLINE, PHAR, WHO

118 REFERENCES IN FILE CA (1967 TO DATE)

© 1993 Education Committee, Division of Chemical Information, American Chemical Society