Intern:International Chemical Identifier

This page is still under work in progress and will contain more elaborate information on so called InChI-strings and keys.

=Definition of InChI-strings and -keys= „InChI“ stands for International Chemical Identifier and was developed by the International Union of Pure and Applied Chemistry (IUPAC) and the National Institute of Standards and Technology (NIST). The InChI-identifiers are now further developed by the non-profit organisation InChI Trust. Both, InChI-string and InChI-key represent identifiers for chemical compounds and shall solve the problem of naming ambiguities (synonyms, different nomenclatures etc.). Thus, the aim of InChI-strings/InChI-keys is to faciliate database linking and data search. The InChI-identifiers are computed by an algorithm from the given chemical structure (independently from the graphical representation). This distinguishes them from other compound IDs (database-, ontology-IDs), which are simply assigned alphanumerical character strings without any encrypted information.

InChI-strings directly encrypt the chemical structure of a compound, whereas InChI-keys are simplified versions computed from InChI-strings. InChI-strings are uniqur and can be easily converted back into a chemical structure, but may be very complex. InChI keys have a defined string length of 27 characters. Due to their simplicity, they are very powerful for database searches. However they can not be reconverted into an InChI-string or the corresponding chemical structure.

=Most important information at a glimpse=


 * Each chemical feature (with defined chemical structure) in the terminology catalogue should contain a standard InChI-key for crosslinking.
 * InChI is non-proprietary and open-source.


 * InChI-strings are unique names/identifiers for chemical structures.
 * InChI-strings are generated computationally from chemical structures.
 * InChI-strings can be turned back into structures.
 * InChI-strings become longer, the more complex the compound is.
 * InChI-strings are not well searchable.


 * InChI-keys have been invented for improved searchability via google and within databases.
 * InChI-keys are calculated from InChI-strings.
 * InChI-keys have a fixed length of 27 characters (letters and dashes).
 * InChI-keys can not be turned back into InChI-strings or structures. This requires a look-up service.


 * InChI-strings and InChI-keys are not ment to be human readable.
 * Standard InChIs should be used for identification and crosslinking between databases

=InChIs in PANGAEA - guidelines=

How to find out InChIs for a given chemical name/structure
Scientists submit data to PANGAEA, which is containing chemical names within parameters (either trivial names, abbreviations, systematic names etc.). Structures are usually only available in corresponding publications (if at all).

The easiest and fastest way to obtain InChIs for terminology catalogue entries is to use the name. If the name can not be used or converted for parsing by a program or the substance can not be found in databases, the structure (if known) can be directly converted into an InChI-string or -key.

Please read the corresponding subchapters.

Please note: It is always recommendable to check InChIs created from names and structures by a database search (do entries contain the right name, structure, synonyms?)

Converting a name into InChI

 * Systematic IUPAC names (best case!)
 * Put the name into a parser like Opsin.
 * Use a drawing tool with integrated parser like BIOVIA Draw (see screenshot).


 * Trivial names, abbreviations, special nomenclatures etc.
 * Search for the name in preferable databases like ChEBI, PubChem, Chemspider etc. (InChIs are provided by most DBs)
 * Convert the name into a systematic name (if nomenclature is known) and use a parser (see above).

Converting a structure into InChI
Please pay attention: Errors are easily made during drawing. Attention should especially be payed to correct connectivity, position of hydrogen atoms and stereochemistry (if given).
 * Use a drawing tool like BIOVIA Draw for drawing and conversion (see screenshot).

=Comparison of InChI - advantages and drawbacks=

=How are InChIs build up?=

=What is the difference between standard and non-standard InChIs?=

=Development= InChI Trust contantly develops and improves InChI functionality.

Recently, the first version of RInChI (Reaction International Chemical Identifier) has been published, an identifier for whole chemical reactions. The structure and functionality of RInChI strings and keys is comparable to normal InChIs.

The trial software version is accessible here.

Publication on RInChI

Other projects aim to solve current drawbacks of InChI:

InChI extension for mixture composition

InChI requirements for organometallics and coordination compounds

InChI requirements for Markush Structures

InChI requirements for polymers

InChI implementation for large molecules

InChI implementation for inorganics

=Database compatibility=

=Resources=
 * InChI Trust FAQ
 * Youtube channel of InChI trust