InChI: open-source chemical structure representation algorithm

InChI Working Groups

InChI Working Groups


Working Group Chair: Leah McEwen

Establish requirements and guidelines for the generation of a unique computer-readable identifier for chemical mixtures for use in chemical stock inventories and information systems based on the InChI standard.

Pseudo-Atom Biopolymer Monomer Atoms

Working Group Chair: Evan Bolton

Efforts towards polymer handling have involved working with the Pistoia Alliance HELM  project to a core set of monomers for amino acids, nucleic acids, and glycans. This  harmonization of core monomers will help to enable use cases for biopolymer handling (i.e.,  input) using a pseudo-atom approach that will sit on top of InChI using the Zz atom.

Markush and Variability

Working Group Chair:  Jonathan Goodman

Working group:
Gerd Blanke, István Öri, Anthony Baston


  • A framework is been defined, based on InChI v1.06
  • Canonicalization and stereo differentiation under examination
  • Creating VInChI: provide a list of InChI and VInChI
  • Creating MarkInChI: currently hand-crafted by artisans

Variability/Positional Isomers (VInChI) 

Working Group Chair: Evan Bolton

How can an InChI provide a canonical encoding of variable  structures?  The working group is assembling test cases, working out what would be useful, and beginning to  focus on the issues that need to be solved to get an effective variable InChI. An ordered list of  InChI addresses many of the criteria, but requires processes to generate it from information  sources and will be unwieldy for the very long lists of molecules which are important use cases.  Various ways of summarizing and compressing are being considered.


Working Group Chair: Gerd Blanke

A standard machine-readable, indexable and searchable representation of chemical reactions based on the IUPAC International Chemical Identifier (InChI).

Extended Tautomers

Working Group Chair: Marc C. Nicklaus

This group is studying how to extend tautomer handling in InChI. Of the 90 tautomeric transforms that were identified, six could be incorporated in an experimental version of the InChI  code (based on InChI version 1.06). See the report “Tautomers in InChI” <link> presented at the March 2021 NIH InChI Workshop <workshop link>.

Extended Stereochemistry

Working Group Chair: Andrey Yerin

The project is making progress and is investigating possible solutions for further consideration. These include enhanced stereo marks; tropisomers; longer allenes; etc.

Organometallics (including Inorganics) 

Organometallics Working Group Chair: Hinnerk Rey

Inorganic Working Group Chair: Richard Hartshorn

The Working Group is currently working slowly towards a proposal to investigate how the  disconnection and reconnection code within InChI affects a set of organometallic compounds.

Large Molecules

 Working Group Chair: Evan Bolton

A presentation titled ‘Progress towards “Large Molecule” support within InChI’ was given at a  recent (March 2021) NIH Workshop on InChI by Evan Bolton.

Education/Academic/Training (OER)

 Working Group Chair: Robert E. Belford

The primary mission of the OER task group is to bring about a greater awareness of InChI in the  education community, while also facilitating its use and adoption across other communities.  There are three major facets to this endeavor; creating original educational material, and creating  a resources that allows educators and scientists to share material with others, with the latter being  the mission of the OER website (, and general outreach (running  workshops, symposia, giving talks, posters, etc).

InChI Source Code Repository (GitHub) 

 Working Group Chair: Gerd Blanke

Having just started, Gerd is in the early stages of assembling this team to review the requirements for an open-source code repository. This must not only support the complex and diverse development community but also protects the InChI assets through the InChI Trust. With a better understanding of the requirements, the group will consider the various options available in terms of languages, development tools and repositories, etc. Given these options, they can then review financial aspects of the various options and work with the InChI supporters and InChI Trust to make recommendations.

QR Codes

Working Group Chairs: Jeremy Frey and Richard Hartshorn

A proof-of-principle implementation was made available: No feedback has been received.

A revised draft of the InChI QR code specification document, formulated as an IUPAC  Recommendation, was prepared and sent out for approval. The recommendation was then  revised and submitted to PAC where it is currently under review.

InChI Resolver

Working Group Chair:  Markus Sitzmann

The InChI Resolver Protocol is a common API protocol which allows any InChI Resolver instance to be findable and browsable for an (automated) client system in a systematic, predefined manner.  It will also allow fort the implementation of a network of federated InChI Resolvers


  • web resources providing data & information based on InChI become findable & interlinked on the web
  • their content is accessible in a generic way
  • (long-term) an autonomous client can find and collect information based in InChI


Working Group Chair: Iseult Lynch

This project proposes to identify a specific nanomaterial/nanoform through an extension of the IUPAC InChI called NInChI.  Their approach is to encode information (composition, size, shape and surface chemistry) required to unambiguously identify these materials. As nanomaterials are particulates, there is an intimate relationship between the core and surface compositions that challenges traditional naming conventions, thereby limiting information exchange among scientists, computational modelers, regulatory agencies and industry. Leveraging best practices with other InChI working groups e.g. Mixture InChI, Reaction InChI & Polymer InChI is planned.


Working Group Chair:  Hunter Moseley

Develop enhanced specifications within the regular InChI standard for representing isotopologues and isotopomers. More specifically, augment the isotopic layer specifications of the regular InChI standard so that specific isotopologues, isotopomers, partial isotopomers, and isotopologue fragments can be represented by a single InChI string and used to identify isotope-informative analytical features.