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IUPAC Chemical Identifier

- a proposal for a unique computerized label -

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The aim of the Chemical Identifier project is to establish a unique label, the IUPAC Chemical Identifier (IChI), which would be a non-proprietary identifier for chemical substances that could be used in printed and electronic data sources thus enabling easier linking of diverse data and information compilations.

IChI will not require the establishment of a registry system. Unlike the CAS Registry System, it will not depend on the existence of a database of unique substance records to establish the next number for any new chemical substance being assigned an IChI. It will use a, yet to be defined, set of IUPAC structure conventions, and rules for normalization and canonicalization of the structure representation to establish the unique label. It will thus enable an automatic conversion of a graphical representation of a chemical substance into the unique IChI label which can be performed anywhere in the world and which could be built into desktop chemical structure drawing packages (such as ChemDraw, ISIS/Draw, etc.) and online chemical structure drawing applets (such as ACD/Draw).

IUPAC would define the process flow leading from input structural information to the creation of the Identifier in three steps: definition of chemical structure input requirements, algorithms for generating a unique set of atom labels (canonicalization), and algorithms for conversion of these labels to the Identifier (serialization). Structure input and conversion to the structural format required by the IChI generator would be done by vendor developed software.

The process would be reversible, so that the Identifier output could be used to recreate structural input information. The Identifier would thus serve as the computer equivalent of the IUPAC name for a molecule. This would facilitate searching the Internet and labeling information in electronic documents with the name of the chemical substance in question.

A. D. McNaught
7 February 2001

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