What is the difference between a chemical and a physical property of a substance? There is no clear-cut answer. In general, you may find one source that calls a given property a physical property and another source that calls it a chemical property. Melting point, boiling point, density, and other such properties typically found in one-volume data handbooks are usually considered physical properties. Other properties, such as reaction yields, types of crystals formed, what solvent a substance dissolves in, etc. are usually thought to be chemical properties. certain types of data are not covered in this chapter. For example, spectral data sources are discussed entirely in the chapter that covers analytical chemistry and constitutional chemistry, and environmentally relevant data sources are found in the chapter on chemical safety or toxicology information.
Physical property data are difficult to find and use. This is especially true since prior to World War II, many of the compilations of property data were published in German. Over time, the names of the properties of interest may have changed, they may be reported in units that are different from those sought, or the conditions (temperature and pressure, for example) under which the published data values were measured do not correspond to those of interest. Sometimes an approximate value is known (or at least a general idea of the magnitude of the expected value) before a data search is begun. Nowadays, there are sources available to predict physicochemical properties based on input parameters.
It is important to remember that data most often appear first in the primary literature, then, through a process of evaluation and selection of the most reliable data, are collected into the various compilations discussed in this chapter. It is not unusual to find several different values for the same physical property, so a choice sometimes has to be made among conflicting values. At such times, the searcher has to take into account several factors, including the reputations of the publishers of the compilations or the reputations of the authors or research institutions that made the original determinations.
There are many one-volume sources of data or handbooks as they are usually called. Frequently the handbooks are derived from (copied from) larger multi-volume data compilations. These larger sources are produced by data centers or information analysis centers whose job it is to critically evaluate the data found in the primary literature. The critically evaluated data compilations may have an indication of the degree of reliability of the data, such as:
The large multi-volume data compilations all provide references to the original primary literature where the data were first published. Small handbooks do not give the original literature citation in most instances, but may indicate where in a large data compilation the copied data are found. Thus, you can track down the original source of data if you suspect an error in transcription may have occurred. For example, Lange's Handbook of Chemistry will refer you to the volume of the Beilstein Handbook of Organic Chemistry for its source of the data, and Beilstein will have the references to the original primary data that they copied.
The printed CRC Handbook of Chemistry and Physics has an appendix, "Sources of Physical and Chemical Data." Included are data journals, data centers, major multi-volume handbook series, selected single-volume handbooks, as well as selected web sites for physical and chemical properties. There are also several books that describe data sources in detail, among them The Search for Data in the Physical and Chemical Sciences (1984) and the CODATA Directory of Data Sources for Science and Technology (1985). Another guide is Handbooks and Tables in Science and Technology (1994). Now that databases have begun to appear with large sets of data in them, it is possible to determine if a particular property exists in a database for a substance of interest. For a given database, such as the Beilstein CrossFire system (or the Beilstein Database on STN), it is possible to search not only for a match of a given substance and a property, but also to search the database for the property itself and a particular value or range of values to identify the substance(s) that match the search criteria.
Landolt-Börnstein (L-B for short) is the largest printed compilation of numerical data in existence today, with over 280 volumes. It covers many areas of interest to chemists, but unfortunately suffers from disuse by many chemists who have not studied German. There are now English-language subject and chemical substance indexes that assist in locating a table in the many volumes of the set. Despite the appearance of a CD-ROM version of the indexes starting in 1996 (including an Index of Organic Compounds), the printed L-B is still a difficult set to use. There is now a full database version on the Web.
Data in Landolt-Börnstein covers:
If you are looking for a physical property of an organic substance or a
two-dimensional depiction of it, the printed Beilstein Handbook of Organic
Chemistry or corresponding database is the place to look. Despite the word
"handbook" in the title, Beilstein is certainly not a one-volume work, not even
a 10-volume work, but one whose volumes number in the hundreds!
the beginning of organic chemistry in the late
18th/early 19th centuries to the present. Although the coverage of the print
volumes got considerably behind the present date, the currency of the database
is quite good, within a year of the current literature. (The printed version is
no longer published.) Not all of the data in the later years may yet have been
critically evaluated, but in many cases Beilstein gives the value(s) for the
physical properties. Even for those properties in the last decade or two that do
not have actual values in the database, an indication that the property may be
found in the primary literature and the references to the original literature
are given.
There are dozens of physical properties reported in Beilstein, and all values are experimental as reported in the original publication. Since it covers millions of organic compounds, it is a prime source for data mining, the use of a database to compile a data set that previously did not exist or to look for data that corroborates a hypothesis one may have formed. Today there are more than 300 million scientifically measured data avaialable in the database.
The capability to search for substances having certain properties or a range of numerical values of properties is inherent in the CrossFire database (and other implementations of the Beilstein database), so it is of particular use in searching for organic materials with a given set of properties. Think of how valuable this might be when combined with the capability to conduct exact structure or substructure searches across the millions of compounds in the database.
Distributed among more than 320,000,000 experimental facts about the compounds are the following types of information in Beilstein:
Compounds are arranged in the printed Beilstein in a manner that keeps acyclic, isocyclic, and heterocyclic compounds together and always in the same relative place in each time period covered. Each compound is assigned to a System Number. For example, System Number 3691 means "heterocyclic carbon frameworks with exactly 2 N ring atoms with a combination of exactly 2 hydroxy groups and 1 carboxylic acid group." The Beilstein system of classifying compounds is reflected in the database by the Lawson Number. The Lawson Number is approximately 8 times as large as the system number. Every substance in the Beilstein file has at least one Lawson Number, and the smaller the Lawson Number, the more common is the fragment. While the Lawson Number is a searchable field, searching with Lawson Numbers is not equivalent to substructure or Markush searching. Since the Lawson Numbers represent certain structural fragments, they can be used for structural similarity searches. Searches that include the Lawson Number are effective when used in combination with other search keys, such as molecular formula, element ranges, etc. They are also useful when combined with NOT logic in substructure searches. Thus, the Lawson Number could serve as an effective index search key if its meaning were known. Fortunately, Allison Tipton's Lawson Number Descriptions translates the numbers for you and gives a link to appropriate Lawson Number ranges for classes of compounds. For example, Carbocyclic Amino Acids are found in Lawson Number range 15976-16119.
Since the original printed Beilstein Handbook is in German, one often encounters German terms or abbreviations to indicate the property reported. Therefore, it is necessary to know the German equivalents of English-language physical property data terms. There is a comprehensive index for the original Beilstein and the first four supplements (coverage through 1959) with a German-language chemical substance name index (v. 28) and a chemical formula index (v. 29). Volumes covering the literature after 1959 are in English.
Here is a link to additional sources of information on Beilstein and CrossFire.
The Chapman & Hall company originally published a series of printed and CD-ROM products with titles that begin Dictionary of ... These are now available online from the CRC CHEMnetBase. The works are really data compilations or larger handbooks, but in a certain sense are dictionaries. That is to say, they tend to collect together in the same section of the printed works chemical substances that are structurally similar and therefore may have similar common names. Particularly significant features of the Dictionary of Organic Compounds are the structural depictions of the substances and properties of derivatives, as well as references to the original literature for synthesis, spectra, etc. of the compound. All of the dictionaries are available in a single database, the Combined Chemical Dictionary, which covers:
Also available is the Merck Index on CD-ROM, and, like the other works discussed in this section, it features the capability to search by structure or substructure of the substance. Both the Merck database and certain of the dictionaries can be found among the database offerings of certain online vendors.
Beilstein does not routinely cover organometallic compounds. Those are the purview of its sister publication, the Gmelin Handbook of Inorganic and Organometallic Chemistry. With the same degree of comprehensiveness as Beilstein, Gmelin supplies the largest single source of information and data on inorganic and organometallic compounds. The arrangement of Gmelin is by element. Information includes:
The Gmelin system ranks substances in order of their tendency to behave as metals. Compounds are arranged in Gmelin according to the principle of last position, determined by the location of the element's number in the Gmelin system. For a given substance, Gmelin provides information on the occurrence, methods of preparation, physical properties, and chemical properties.
Gmelin is available as an online database on some commercial vendors' systems, but is also being marketed now as a database that can be searched by structure and other parameters using the same CrossFire system used to search the Beilstein CrossFireplusReactions database. It is also offered through Elsevier MDL's DiscoveryGate package.
Many books (monographs, treatises, and textbooks) include tables of data. Unfortunately, there is no comprehensive index that might tell you which book has a particular data compilation. Sometimes a general search of a library's OPAC (online catalog) for a class of compounds will turn up promising titles that can be checked for data. Treatises, since they cover broad subject areas, are potentially very good sources, but are often poorly indexed or lack a comprehensive index for the entire set.
Encyclopedias, on the other hand, are excellent sources of physical property information. The most important chemical encyclopedia is the Kirk-Othmer Encyclopedia of Chemical Technology, now in its 5th edition. This work is also available as a CD-ROM product and as an online or Web database.
Other examples of encyclopedias relevant to this area are the Encyclopedia of Physical Science and Technology (3rd ed., 2002) and such specialized encyclopedias as the Polymeric Materials Encyclopedia (1996) and the Encyclopedia of Advanced Materials (1994).
It would seem that journal articles would be excellent sources of physical property data, and for standard data that are routinely reported, they are. The problem is that indexing of physical property data contained in journal articles is not always well done by the abstracting and indexing services. However, there are some journals that are specifically designed to publish data. Two of those are the Journal of Physical and Chemical Reference Data(1972-) and the Journal of Chemical and Engineering Data (1956-). The former title has comprehensive printed indexes for each group of 10 volumes. Sometimes, an earlier, separately published work will be updated in a journal article or articles. For example, the 1958 Chemical Society publication Tables of Interatomic Distances and Configurations in Molecules and Ions (Special Publication no. 11 and its supplement Special Publication no. 18 published in 1965) was updated in the Journal of the Chemical Society, Perkin Transactions 2 1987, Supplement pages S1-S19 for the organic portion and in the Journal of the Chemical Society, Dalton Transactions 1989 Supplement pages S1-S83 for the organometallic and coordination complexes.
One technique to locate data in journal articles is to perform a search that includes terms in the abstracts of the articles in a bibliographic database such as the Chemical Abstracts CA File on STN or SciFinder. Frequently, the actual values of the most important data will be included in the abstracts. Another technique is to search the fulltext files of the electronic versions of the journals themselves. As more and more scientific journals become available in electronic format, this should prove to be an increasingly important approach, especially as vendors find more innovative ways to search across journal titles. Previously published in microform, the Supporting Information for articles published in ACS journals is now online and linked to the references that have such data. This is data that is too voluminous to publish in the articles themselves. A number of other publishers take similar approaches.
There are many, many handbooks published in science and technology. Perhaps the best known of those in the physical sciences is the CRC Handbook of Chemistry and Physics (now published annually). The CRC Press publishes dozens of handbooks in various areas and has produced a Composite Index for CRC Handbooks (1991) that leads to the appropriate work where a substance and a property may be found. There is also a CD-ROM version of this title. Other famous one-volume handbooks are:
Some of these are now made available on the Web by Knovel.
The user of more general one-volume handbooks such as Lange's or the CRC, should be aware that they cover only the most common 10,000-15,000 chemical substances and include for the most part the same data for those compounds. Furthermore, they all take the data from standard sources such as Beilstein or Gmelin. Hence, it is usually not productive to search through many of them in hopes of finding a value when one handbook has failed to provide the answer. If possible, start your search with larger sources such as Beilstein, Gmelin, or the Chapman & Hall/CRC dictionaries. If those are not available, you will find larger numbers of substances covered in some of the specialized sets, such as the 3-volume Handbook of Data on Common Organic Compounds (1995). Corresponding to that work is v. 5.0 of the CD-ROM product Properties of Organic Compounds, a database covering over 27,000 organic compounds that is searchable by structure.
A much larger number of chemical substances can be found by using ChemFinder.Com on the Web courtesy of CambridgeSoft. ChemFinder.Com has over 75,000 compounds taken from over 350 indexed sites. It offers several modes of searching, including name, molecular formula, molecular weight, CAS Registry Number, and structure. The NIST Chemistry WebBook is another popular Web site that has data for over 7,000 organic and inorganic compounds. Also included are thermochemical and spectral data. NIST is the National Institute of Standards and Technology (formerly, the US National Bureau of Standards). It publishes a number of data compilations and Standard Reference Data Sets.
Another interesting Web site, though with relatively few compounds (2483 currently) is the Organic Compounds Database at Colby College. It is searched by name, molecular formula, or data values for properties such as melting point, index of refraction, formula, absorption wavelengths, mass spectral peaks, and type of chemical substance.
Perry's Chemical Engineers Handbook is one of many tools available from Knovel. It covers thousands of facts, figures, formulas, tables, graphs, and calculations for chemistry and physics. Exact values or ranges of values of physical properties can be used as search keys, in addition to names of substances or physical properties. Also found on Knovel are the Lange's Handbook of Chemistry and the Chemical Properties Handbook.
Knovel has done a great service to the scientific community by providing free versions of some standard physical property sources. They are:
Free Databases from Knovel
ICT is a perennial favorite found on the reference shelves in most libraries. Originally published for the National Research Council, ICT offers data on physical, thermodynamic, mechanical, and other key properties and is a major reference source used by those involved in chemistry, physics, and engineering. The full text of the original print version is also available (full-text searchable). All entries in the index are hyperlinked to their page numbers. Interactive tables include: