Chemical Literature (Chem 184/284)

Lecture 11: Chemical Abstracts, Part 1: Print

Chemical Abstracts Service: http://www.cas.org

• Chemical Abstracts Service was founded in 1907 as a division of the American Chemical Society.
• The first volume contained 15,000 abstracts and was distributed free of charge to ACS members. Indexing and abstracting was done by professional chemists acting as volunteers.
• Today: over 1,000,000 abstracts per year, with indexing done by a team of dozens of professional indexers, most with PhDs in chemistry or related sciences, and hundreds of support staff; annual subscription in print-- over $30,000 for 2008.
• About 27 million abstracts total have been published (as of January, 2008.)

What CAS Does

• CAS attempts to comprehensively index the chemical literature, including:
  • Over 10,000 journals; about 1,500 of which are now indexed cover to cover -- covering documents of chemical importance
  • patents from over 50 national patent offices, three international organizations and two types of non-patent invention disclosures
  • technical reports, conference papers, books and dissertations.
  • electronic journals and preprint servers
  • meeting abstracts from ACS national meetings

Other CAS Services

• Chemical Industry Notes (CIN) -- indexes the literature of chemical business (e.g. Chemical & Engineering News, Chemical Week.)
• CAS Registry Service
  • Started to track chemical substances for CAS internal files; now the standard method for uniquely identifying chemicals, used as an indexing tool by many chemical reference sources.
  • All substances indexed by CAS get RN's, plus substances submitted by outside firms or agencies
  • Every chemically distinct substance gets its own Registry Number, including stereoisomers, isotopically labeled substances, mixtures, polynucleotide and protein sequences, etc.
  • As of January, 2008, over 33 million simple organic and inorganic substances, and almost 60 million biosequences (polynucleotides and polypeptides) have been registered.
  • Registry Numbers are of the form: xxxxxxx-xx-x The number of digits in the first group may vary, but the second and third groups are always two digits and one digit.
  • The Registry Number has no chemical meaning; you can't tell from the RN what kind of compound it refers to.
• Chemical Abstracts Service Source Index (CASSI)
  • Lists all periodicals ever indexed by CAS
  • Lists many pre-1907 sources, such as those appearing in Beilstein
  • Available in print or on CD-ROM
  • Periodicals are listed in alphabetical order by their abbreviations -- the name appears in full, with the abbreviated portion in boldface.
  • Listings include language information, starting dates and current volume numbers, cross-references to changed titles or translations and holdings information.
• CAS Document Detective Service
  • provides copies of documents indexed by CA or CIN, generally from 1975-present.
  • Exceptions: indirectly indexed documents, like tech reports or dissertations
  • If copyright is a problem, they will lend the original.
  • If they don't have it themselves, they will forward the request to the British Library Document Supply Centre.
• Science IP -- The CAS Search Service
  • Professional scientific searching on a task-by-task basis, by the highly trained information professionals at CAS.
• CAS Client Services
  • Contract services including inventory control, substance identification and Registry number assignment.

Importance of Chemical Abstracts

• Scope
  • CA attempts to cover chemistry in the broad sense...anything that might be interpreted as new research in chemistry or chemical engineering
  • Chemistry as the "central science". CA's coverage has high overlap with medicine, biology, physics, materials, agriculture, geology, etc., making it important for researchers in those fields as well.
  • Note: since CA focuses on "new research" in earlier times it did not index all chemical patents - only those deemed to have "new chemistry".
• Comprehensiveness
  • CA attempts to cover the literature of chemistry worldwide, in any language.
  • It attempts to cover all forms of primary chemical literature.
  • Note that in some cases - technical reports and dissertations - it depends on secondary sources and indexers do not read the original documents.
• Chronological coverage
  • Print CA began in 1907; electronic CA in 1967 -- but now the whole CA collection back to 1907 has been digitized, and CAS has added to the electronic database selected records from 1876 to 1906 including the early issues of JACS and J. Phys. Chem.. It is now adding records from Chemisches Zentralblatt, an early chemical literature index, which will eventually cover 1830-1906.
  • Abstracts are added to the print sections every week; in online form, updates are daily. Online, basic bibliographic information for the 1500 core journals and nine key patent authorities is online within two days after receipt at CAS. Other types of documents, especially technical reports and dissertations, may have a significantly greater time lag.
  • Print abstracts get keyword indexing when published; detailed indexing when a volume is completed and indexes are cumulated every ten volumes. Electronic abstracts have detailed indexing added as it becomes available. Online records are first added with bibliographic data and abstracs only; detailed indexing is added as it is completed.
• Access points
  • Weekly issues index by author, keyword and patent number (see below for details.)
  • Volume indexes index by author, subject heading, systematic chemical name, molecular formula and patent number (see below).
  • Electronic forms combine keyword and subject heading approaches, and add roles for chemical substances.
  • In the online form, links to Registry File add enhanced searching of chemical substances, including structure searching.
  • The online version of the database also has cited references for journal articles, conference paprs and patents from key issuing authorities from 1997 on.
• Constant enhancements: CAS has been in forefront of computerization of indexing for over 30 years and is always refining its search tools.

Chemical Abstracts in Print

Why Devote a Lecture to Chemical Abstracts in Print?

• Not all institutions/businesses will have ready access to electronic CA. You may have to use the print form, if not here, then elsewhere in your career.
• Perhaps more importantly, some of the characteristics of indexing in CA were born in the print medium, and still affect the way you search in the electronic form. For example, searching by chemical name in SciFinder Scholar is still affected by the nomenclature rules developed for CA in print.

Arrangement of Abstracts in Print CA

• For ease of browsing, abstracts are grouped by subject area.
• Currently there are 80 subject sections (see http://www.cas.org/products/print/ca/casections.html), divided into five broad groups.
  • Biochemistry
  • Organic Chemistry
  • Macromolecular Chemistry
  • Applied Chemistry
  • Physical, Inorganic and Analytical Chemistry
• Biochemistry and Organic Chemistry used to come out in odd-numbered weeks, while Macromolecular Chemistry, Applied Chemistry and Chemical Engineering and Physical, Inorganic and Analytical Chem. used to come in even-numbered weeks. Now, abstracts are added in all sections each week.
• Cross-references are used where a given abstract might legitimately appear in more than one section.
• Note that subject sections change with time to reflect current research.
• Subject Coverage Manual gives a detailed definition of each section, and a table of changes over the years.
• One volume per year was published until 1962, when they switched to two volumes per year. Collective Indexes where issued every ten years until 1957, and every five years since then.
• Abstracts have been individually numbered only since 1967. From 1907-1932, pages were numbered, and indexes would refer to a page number, with a superscript denoting the order of the abstract on the page. Example: 321⁶, for the sixth abstract on page 321.
  From 1933-1966, each page had two columns of abstracts which were numbered, with letters running down the center of the page to identify where on the page the abstract fell. Example: 1733h would be near the bottom of page 1733.
  Since 1967, abstract numbers have been of the form 223717w, where the letter is meaningless except as a sort of check digit.

Contents of the Abstract Record

• All CA records contain:
  • Title of the document
  • Author(s) or inventor(s) for patents
  • Corporate source or patent assignee information
  • Source Information, e.g. journal title, volume, issue, pages or patent numbers
  • Language
  • Abstracts (usually)
• Author's names appear as given in the original document.
• Abstracts for journal articles are usually those written by the author.
• Patent abstracts may be fleshed out by the indexer.
• Dissertations and some other documents have no abstracts.
• Note that in the early days of CA, the abstracts tended to be much longer and more detailed; nowadays, the abstracts are usually the same as those in the published paper.

Abbreviations

• Journal names are listed using CASSI abbreviations.
• Corporate names are heavily abbreviated.
• All abstracts use abbreviations for common chemical terms (see CAS Standard Abbreviations and Acronyms at http://www.cas.org/products/print/ca/standabbrevacro.html.)

Indexing in Print CA

• The types of indexing available in CA reflect the constraints of print.
• The indexing available in the weekly issues is that which can be done most quickly.
• The indexing in the Volume and Collective Indexes is more systematic, but still reflects the limitations of print.
• Issue Indexes
  • Author
  • Keyword
  • Patent
• Volume & Collective Indexes
  • Author
  • Chemical Substance
  • General Subject
  • Molecular Formula
  • Patent

Author Indexing

• Weekly Issues
  • All authors are listed by last name and initials only. The index gives only the abstract number. Examples:
    • Lipshutz B H 151869t
    • Little R D 152780u
  • Patents have entries for both inventor and assignee; their abstract numbers have P before the number. Examples:
    • Genentech, Inc. P146735s
    • Leong S R P 146735s
  • Other types of corporate authors, such as societies and government agencies, also get author entries
    • United States Food and Drug Administration 150996v 150997w
• Volume and Collective Indexes
  • First authors get both the abstract number and title of the paper listed under their names.
  • The author name is not necessarily the form used in the article, but may be a standardized form of the name. (Note: in recent years, CAS has largely given up on name standardization and uses the form found in the document.)
  • Other authors are cross-referenced to the first author of the document.
  • Examples:
    • Ford, Peter Campbell
      Quantitative mechanistic studies of the photoreactions of... 148754a
    • Lange, Frederick Fouse
      See Miller, Kelly T.; Sudre, Olivier
      ---; Lam, D.C.C.; Sudre, O.
      Powder processing and densification of ceramics 144196x
  • Even though CA tries to pull all of an author's works under one name, it cannot always distinguish authors with the same initials, so it alphabetizes by last name and initials, even where the full name is spelled out! Examples:
    • Ellis, A.
    • Ellis, Arthur Baron
    • Ellis, A. D.
    • Ellis, Anthony Ewart
    • Ellis, Avery K.
    • Ellis, Andrew Michael
    • Ellis, Albert T.
• Spelling of Author Names: Be aware of special rules for handling certain names. Names with "Mc" or umlauted letters or transliteration from non-Roman alphabets can be tricky. Example:
  • Mössbauer is listed as Moessbauer

Patent Indexing

• Chemical Abstracts only indexes the first version of each patent it receives.
• However, the patent index (arranged by country code and patent number) gives cross-references from later, equivalent patents, that is, the same invention by the same inventor, patented in a different national or international patent office..
• When searching for an equivalent patent, start at the year of issue of the known patent reference and work forward until you find the equivalent or run out of indexes.

Concept Indexing in Chemical Abstracts

• 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.

Keyword Indexing

• 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
  Article title: "Facile preparations of 4-fluororesorcinol"
  • Acetophenone
    methoxy fluorination regiochem
  • Benzene
    fluoro dihydroxy
  • Deacetylation
    demethylation fluorodimethoxyacetophenone
  • Demethylation
    fluorodimethoxybenzene
  • Methoxybenzene
    methoxyacetophenone fluorination regiochem
  • Fluorodihydroxybenzene
  • Fluororesorcinol
  • Resorcinol
    fluoro

Volume and Collective Indexes: General Subject Index

• 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. In 1997, headings were changed to be more like natural language for easier electronic searching, with the print version treated as a secondary aspect of CA. However, these new headings in turn proved unpopular, and many changed back in 1999.
• Note: to help cope with these changes, CAS has developed an electronic thesaurus, called CA Lexicon, which is available as part of the CA Databases on STN. It currently covers the subject headings from 1967-present. Presumably, as the subject indexing from 1907-1967 is added to the electronic files, the Lexicon will be expanded to cover the chronological changes. It has not yet been fully implemented for SciFinder or SciFinder Scholar.
• However, CAS has used the Lexicon to algorithmically change the subject headings in the electronic files for 1997-1998 to conform with the previous and subsequent versions. Moreover, SciFinder Scholar has some built-in synonym checking which carries out part of the functions of the Lexicon, at least for commonly used synonyms (e.g. cancer, carcinoma, neoplasm.)
• Broadly speaking, the General Subject Index includes:
  • classes of chemical substances
  • physical and chemical phenomena
  • types of reactions
  • chemical technology
  • industrial processes and equipment
  • scientific names for living organisms
  • biological and medical terminology
• For extensive subjects, qualifiers were added as part of the main subject heading, such as Blood, analysis. For 1997-98, the qualifiers become part of a single heading: Blood analysis. In 1999, the system reverted to the pre-1997 standard.
• Pre-1997, classes of substances used to have derivative categories, such as Carboxylic acids, esters. From 1997-98, there is simply a heading for Carboxylic acid esters. In 1999, the pattern reverted.
• Classes of compounds in both periods have qualifiers, but the specific qualifiers have changed. Sulfonic acids, uses and miscellaneous was the old usage. Now, Sulfonic acids, miscellaneous and Sulfonic acids, uses are separate. This change has not reverted.
• Note: the following list of substance categories apply to pre-1997 indexes and post-1998 indexes. In the two year interval, most were replaced by separate headings.
• Substance Categories
  • For ketones, aldehydes
    - acetals, hydrazones, mercaptals, oximes
  • For acids
    - anhydrides, anhydrosulfides, esters, lactones
  • For alcohols
    - ethers
  • For amines
    - oxides
  • General: compounds, derivatives, polymers
• Heading Qualifiers (old)
  • For substances and classes of substances
    
    • analysis
    • biological studies
    • occurrence
    • preparations
    • properties
    • reactions
    • uses and miscellaneous
    • New: all of the above, plus formation (nonpreparative) and processes, as well as separate uses and miscellaneous categories.
  • In the electronic versions of the file, these have evolved into role indicators.
  • For organs and tissues (old)
    • composition
    • disease or disorder
    • metabolism
    • neoplasm
    • toxic chemical or physical damage
  • In 1997-98 subject headings, the disease and neoplasm headings have been combined with their respective organ or tissue to form separate primary headings.
  • For alloys (old)
    • base - applied to the largest single constituent of the alloy.
    • non-base -- applied to other constituents of the alloy.
  • Most alloys are now listed by type not constituent; to search by constituents, use the Chemical Substance Index.

CA Index Guide

• The Index Guide is the key printed tool for identifying the correct subject heading for any topic in Chemical Abstracts
• 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!

The Rule of Specificity

• 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 most indexes, cancer of the lungs will appear as Lung, neoplasm not Lung, disease.
• From 1997-98, the general term in Lung tumors with more specific terms for specific types, e.g. Lung adrenocarcinomas

Substance Indexing: The Challenge of Nomenclature

• In order to ensure that each substance has a unique possible name, and to group "like" compounds together, CA has devised their own system of nomenclature (not necessarily IUPAC) and scheme for arranging them in the Chemical Substance Index.
• Unfortunately, this system can be hideously complex. Here's a hideous example
  • Dodecahedrane (C20H20) used to be listed as simply dodecahedrane.
  • Then a systematic name was assigned:
    5,2,1,6,3,4-[2,3]Butanylidenedipentaleno [2,1,6-cde:2',1',6'-gha]pentalene, hexadecahydro-
  • Now it's treated as a member of the fullerene family:
    [5]Fullerane-C20-Ih
• It is important to remember that the CAS nomenclature has changed over time, as in the case of dodecahedrane above. The most important change took place in 1972; nomenclature has been fairly stable since then. But if you are using the older literature, you may have to do some checking to be sure of the correct terminology.

Basic Rules of CAS Nomenclature

• CAS indexers select the "main" part of the compound to act as the heading parent.
• Substituents to the parent are listed after it. This is referred to as inverted order
• What constitutes a parent compound and how it would be named are not always obvious, even to a chemist.
• Examples
  • Toluene is
    Benzene, methyl-
  • ortho-Xylene is
    Benzene, 1,2-dimethyl-
  • Benzyl alcohol is
    Benzenemethanol
• When there are multiple substituents, they are listed in alphabetical order, including the prefixes.
  • Carbon tetrachloride is
    Methane, tetrachloro-
  • CCl₂F₂ is
    Methane, dichlorodifluoro-
  • CCl₃F is
    Methane, fluorotrichloro-
• Polymers are listed by the monomer(s) or repeating unit, with polymer or homopolymer appended.
  • Teflon is
    Ethene, tetrafluoro-, homopolymer

Alphabetization of Compounds

• Compounds are listed first by parent compound, with the parent compound itself first (with any qualifiers and categories), then by substituted forms in alphabetical order.
• Substituents are read from left to right, ignoring numbers and punctuation.
• Example: Benzene
  • Benzene
  • Benzene, analysis
  • Benzene, uses and miscellaneous
  • Benzene, compounds
  • Benzene, polymers
  • Benzene, azido-
  • Benzene, chloro-
  • Benzene, 1,2-dibutyl-

Special Cases: Salts

• Salts of organic acids, or inorganic oxyacids are named as derivatives of the parent acid.
• Potassium chloride is
  Potassium chloride
• But: Potassium sulfate is
  Sulfuric acid, potassium salt (2:1)

Helps for finding CAS Chemical Names

• In general, it can be very tricky to look at the structure of a complex compound and decide what the CA name will be.
• However, in many cases, you can use a variety of resources to help find the CA name.
• Remember that some data collections give the CAS name for compounds: Merck Index, CRC Handbook of Chemistry and Physics, among others.

Using the Index Guide for Chemical Names

• If the compound has a common or trade name, check the Index Guide.
• The Index Guide is especially good for drugs, natural products, dyes, etc.
• For other common chemicals, even if you can't find the specific chemical you want, you may be able to find a similar one and get a clue to follow.

Using the Registry Number Handbook for Chemical Names

• Searching by compound Registry Number is a preferred approach when using any of the electronic forms of CA. However, there is no Registry Number index for printed CA.
• CAS publishes a "handbook" which lists Registry Numbers and gives the CAS systematic name for the substance.
• Remember that there are many sources you can use to find Registry Numbers which have good synonym indexes: Merck Index, HODOC, Combined Chemical Dictionaries (or the print equivalents), the Aldrich catalog,ChemFinder, Kirk-Othmer, etc.
• On the other hand, you should also remember that different sources may give different Registry Numbers for what appears to be the same substance: examples: parent compounds with salts, stereoisomers, polymers.
• The UCSB library's copy of the Registry Number Handbook is shelved just after Chemical Abstracts itself.

Molecular Formula Index

• While most molecular formulas have a large number of possible compounds. it is far easier to look at a possible name and decide whether it matches your compound than to guess at a name.
• Note that the Molecular Formula Index just gives a list of abstract numbers, not a breakdown by subheadings.

Molecular Formula Index Organization

• Molecular formulas are listed in Hill order:
  1. If carbon is present, it comes first, followed by hydrogen, then all other elements in alphabetical order.
  2. If not, then all (including H) in alphabetical order.
• Note that the rules for salts apply to molecular formulas, too.
• Molecular Formula Examples
  • Benzene is C₆H₆
  • Teflon is (C₂F₄)x
  • Ferrocene is C₁₀H₁₀Fe
  • Hydrochloric acid is ClH
  • Benzoic acid is C₇H₆O₂
  • Sodium benzoate is C₇H₆O₂, sodium salt...NOT C₇H₆NaO₂

Using the Ring System Handbook for Chemical Names

• Most compounds with a polycyclic ring system use the name of the ring system as the parent compound.
• The Handbook lists ring systems in order of:
  • Increasing number of rings
  • Increasing number of atoms in the ring
  • Increasing Hill order formula of the ring
  • Example:
    
    
  • Step 1: Count number of rings, using the smallest rings in the structure which will take in all the atoms in the ring system - 5
  • Step 2: Count the number of atoms in each ring - 5, 6, 6, 5, 5
  • Step 3: Note the "molecular formula" of each ring - C₅, C₆, C₅O, C₄O, C₅
  • Step 4: Arrange the formulas in order of increasing size and Hill order: C₄O, C₅, C₅, C₅O, C₆
  • Step 5: Look up the ring systems that fit the formula and pick the correct one by inspection (not always easy).
  • Resulting name: 5H-4a,11a-epoxy-7,9a-methano-1H-cyclopenta[b]heptalene
• The entry for a given ring system gives structure diagram with CAS locant numbers, name, Registry Number of the parent ring.
• Rings which are less unsaturated will (for complex rings) have the same parent name, but with, for example, "decahydro" added.

When print tools fail you...

• Even with all of the above, sometimes none of the tools will help you find the correct name.
• And if you don't find something, does it mean that you haven't guessed the right name, or that it hasn't been reported??
• Enter the power of computer searching - structure searching can give a definitive answer to most questions.

This page created by Chuck Huber (huber@library.ucsb.edu).
Updated: 02/08/08 01:47:58