About the InChI Standard

A few general questions and answers about the InChI are supplemented by an extensive technical FAQ available here.

What is an InChI?

InChI is short for International Chemical Identifier.

InChIs are text strings comprising different layers and sublayers of information separated by slashes (/). Each InChI strings starts with the InChI version number followed by the main layer. This main layer contains sublayers for chemical formula, atom connections and hydrogen atoms. Depending on the structure of the molecule the main layer may be followed by additional layers e. g. for charge, stereochemical and/or isotop information.

History of InChI

1999: Steve Heller initiated a proposal at the National Institute of Standards and Technology (NIST) for a public domain structure representation standard for the NIST databases, along with Steve Stein who was the initial designer and architect for the project.

2000: from a meeting with a wide range of users of chemical nomenclature including database providers, patent officials, international trade representatives, et al, under the direction of Alan McNaught, it was decided that InChI would be an IUPAC initiative to meet the needs of the chemical and related communities.

2001: the IUPAC Chemical Identifier project began in collaboration with the US National Institute of Standards and Technology (NIST). The aim was to devise a computer based algorithm yielding a unique label for any chemical structure, regardless of how it was represented (on screen).

2005 (April): version 1 of the IUPAC International Chemical Identifier (InChI) was launched. The development and associated programming work was predominantly carried out by Dmitrii Tchekhovskoi.

2008: a shorter hash key version of InChI, known as InChIKey was developed by Igor Pletnev. This alternative format is much more suitable for use in search engines and offers many new possibilities for software applications.

2009 (January): standard versions of InChI and the InChIKey were released, which took the original algorithm with its many variable parameters and fixed them so that interoperability between databases and resources with InChIs could be achieved.

2009 (July): the InChI Trust was formed. The 2009 Board of Directors consists of 8 members: The Royal Society of Chemistry • Nature Publishing Group • Elsevier Properties SA • Thomson Reuters • John Wiley & Sons • FIZ CHEMIE • Taylor & Francis • IUPAC.

2011: version 1.04 of the InChI software was released as well as an InChI Certification Suite which is designed to check the correct installation of the InChI software. Certification logos for correct installations as well as InChI Trust member and supporter logos are provided by the InChI Trust.