Chemical Literature (Chem 184/284)

Lecture 10: Chemical Abstracts in Print, Part 2

Weekly issues use keyword indexing assigned by the indexer. Terms are not systematically selected.
Volume and Collective Indexes use systematic indexing for both general concepts and chemical substances.

Keywords are assigned by the indexer based on the body of the document, not just the title or abstract.
Terms are often abbreviated, following the standard CA abbreviations
To save space, a keyword is not assigned if it's part of the section heading for the section the abstract appears in, e.g. "Steroids".
Additional keywords are listed beneath the main keyword heading to flesh out the concept (like the co-terms in Science Citation Index).
Chemical names are listed along with concept terms in the issue indexes. The chemical names are not systematic, but follow the author's nomenclature.
Example

The General Subject Index uses standard subject headings in order to better bring related documents together (collation).
The standard headings list does get modified and expanded to reflect new areas of research. Major changes are usually done at the beginning of a Collective Index period. Sometimes the changes are minor, sometimes drastic.
Prior to 1997, headings were chosen so as to draw related topics into physical proximity in the printed volumes, with electronic searching treated as a secondary aspect of CA. Starting in 1997, headings have been changed to be more like natural language for easier electronic searching, with the print version treated as a secondary aspect of CA.
For examples of the 1997 changes see the CAS General Subject Vocabulary Helper at http://www.cas.org/vocabulary/
Broadly speaking, the General Subject Index includes:

For extensive subjects, qualifiers are added as part of the main subject heading, such as

Note: the following lists of categories apply to pre-1997 indexes. Some are undergoing dramatic changes.
Substance Categories

acetals, hydrazones, mercaptals, oximes

anhydrides, anhydrosulfides, esters, lactones

ethers

oxides

In the electronic versions of the file, these have evolved into role indicators.
For organs and tissues

In post-1997 subject headings, the disease and neoplasm headings have been combined with their respective organ or tissue to form separate primary headings.
For alloys

The Index Guide is the key printed tool for identifying the correct subject heading for any topic in Chemical Abstrancts
Each Index Guide lists the approved headings in use for its period of coverage.
An IG is published at the beginning of each Collective Index period, with updates every 18 months until the final comes with the Collective Index itself.
Contents of the Index Guide

An alphabetical listing of the approved subject headings, with cross-references to related headings and descriptive notes.
Many common terms not used as headings are listed, with See references to the correct heading.
Many common and/or trade names for chemical substances are listed, giving the correct CA systematic name (and Registry Number!)
There are also appendices on the organization and use of the subject indexes; how CA indexers select headings; CA chemical nomenclature; and a hierarchical list of the headings.

Whenever you are doing a subject search, in print or online, it's a good idea to check the Index Guide!! And be sure to check the correct Index Guide for the years you are searching!

Usually, CA indexers will assign the most specific subject heading that applies to the document.
For example, if a document deals with the synthesis of a specific ester, the indexer will assign that substance to the index, not the general term "Esters".
In pre-1997 indexes, cancer of the lungs will appear as Lung, neoplasm not Lung, disease.
From 1997 to the present, the general term in Lung tumors with more specific terms for specific types, e.g. Lung adrenocarcinomas