NIST Chemistry Webbook and IUPAC International Chemical Identifier

The NIST Chemistry WebBook is a site on the Internet (http://webbook.nist.gov/) that provides convenient access to a variety of physical and chemical property data on well defined chemical species and reactions. The site is used by scientists, engineers, educators and the general public.

The IUPAC International Chemical Identifier (InChI) is a tool that has been developed to provide a modern tool for the identification of chemical species. Because InChI is derived via software from the structure of a molecular species, it is not dependent on third party registries or arcane nomenclature rules.

These two efforts are complementary: the WebBook tests and publicizes the technology behind InChI. InChI development work provides tools that help integrate the databases in the WebBook.

Intended Impact

It is part of NIST’s mission to distribute Standard Reference Data® to scientists, engineers, educators, and the general public. The NIST Chemistry WebBook is intended to help fulfill NIST’s mission by distributing such data over the Internet.

It is also part of NIST’s mission to work with standards bodies to develop standards to promote science and commerce. Work with IUPAC on InChI is intended to provide a standard that will make it easier for chemical species (and by extension mixtures and reactions) to be reliably identified.

Objective

Develop a web site that provides reliable and convenient access to NIST data on chemical systems. Work with an appropriate standards body to develop a standard to aid in the dissemination and interchange of data for chemical systems.

Goals

• Distribute NIST data for chemical systems in manner that is convenient for NIST’s customers.
  
• Work with IUPAC to develop and improve a data standard for the representation of chemical species based on their structure.

Research Activities and Technical Approach

The NIST Chemistry WebBook was established in 1996 and has grown to encompass a wide variety of thermochemical, ion energetics, physical, solubility, spectroscopic, and chromatographic data. It includes a variety of data from NIST and outside contributors. The site also includes two special features: a set of interactive physical property models developed at the NIST Boulder labs and a group additivity based estimator for gas phase thermodynamic properties. The many contributors to the WebBook are identified in the “credits” section of the web page at http://webbook.nist.gov/chemistry/.

The greatest technical challenge in the development of the WebBook is the integration of databases from multiple sources into a single collection of data. Problems with integrating these data sets are exacerbated problems associated with the identification of chemical species: inconsistent nomenclature, ambiguous or erroneous references to third party registries, and inconsistent conventions for chemical formulas. The development of InChI has been a response to these problems.

InChI is a text string that is produced by software from the structure of a chemical species. The software that generates InChI strings was largely developed at NIST and incorporates normalization and canonicalization algorithms to generate the identifier. Because of this approach, the InChI string is largely invariant to the manner in that the species was drawn.

The InChI string is constructed in a modular (layered) approach. Information derived from the structure is placed in different parts of the string based on its type. An InChI string contains sections (layers) for properties such as bulk formula, connectivity, and geometric stereochemistry. Comparison of two InChI strings can thus produce information about the associated species. Species with identical InChI strings are the same. Species that differ only in their geometric stereochemistry layers are stereoisomers.

Use of InChI in the WebBook site is illustrated in figure 1. This example shows how InChI strings are distributed by the site and how it is used to identify related chemical species: optical isomers.

• The NIST Chemistry WebBook receives more than two million page views per month.
  
• Updates of the WebBook include new energy level, gas chromatography, ion thermochemistry and mass spectral data.
  
• InChI standard has been ratified by IUPAC (development of future versions is ongoing).