International Chemical Identifier

Encyclopedia : I : IN : INT : International Chemical Identifier

The IUPAC International Chemical Identifier (InChI), developed by IUPAC and NIST, is a digital equivalent of the IUPAC name for any particular covalent compound. Chemical structures are expressed in terms of five layers of information – connectivity, tautomeric, isotopic, stereochemical, and electronic.

The InChI algorithm converts input structural information into the identifier in a three-step process: normalization (to remove redundant information), canonicalization (to generate a unique set of atom labels), and serialization (to give a string of characters).

Contents

1 Examples
2 Layer types
3 Sub-layers
4 Notation
5 See also
6 External links

Examples

CH₃CH₂OH
ethanol InChI=1/C2H6O/c1-2-3/h3H,2H2,1H3

L-ascorbic acid InChI=1/C6H8O6/c7-1-2(8)5-3(9)4(10)6(11)12-5/h2,5,7-10H,1H2/t2-,5+/m0/s1

Layer types

There are six InChI layer types:

Main layer
Charge layer
Stereochemical layer
Isotopic layer
Fixed-H layer
Reconnected Layer

Sub-layers

Each layer can be split into sub-layers. For example, the main layer can be split up into three sub-layers:

Chemical formula (no prefix)
Atom connections (prefix: "c")
Hydrogen atoms (prefix: "h")

Notation

Layers and sub-layers are both separated by the "/" delimiter. All layers and sub-layers (except for the chemical formula sub-layer of the main layer) start with a lower-case letter indicating the type of information held in that layer.

External links

[IUPAC InChI site]
[InChI.info] - an unofficial InChI website featuring on-line converter from InChI to molecular drawings
[Unofficial InChI FAQ]
[Generate InChI] (interactive service at University of Cambridge, either interactive or WSDL)
[Search Google for molecules] (generates InChI from interactive chemical and searches Google for any pages with embedded InChIs). Requires Javascript enabled on browser
[PubChem online molecule editor] that supports SMILES/SMARTS and InChI
[MarvinSketch] implementation to draw structures (or open other file formats) and output to InChI file format

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