International Chemical Identifier (InChI)

InChI string/keys are text identifiers for small organic molecules, and are generated from structural diagrams. There is generally no need for special drawing conventions. InChI is quite robust with respect to the many different ways of drawing the same chemical compound.

However, one limitation is that it covers mainly organic compounds; inorganic and organometallic compounds can be converted, but in such cases (currently) chemically different compounds can get the same InChI string/key under certain circumstances.

Furthermore, non tetrahedral stereochemistry (anything else than R and S) is not taken into account.

Structure Drawing Tools
Since Elsevier processes and generates InChI strings/keys internally, every structure editor that has the ability to export a given compound as MOL file is suitable, provided that the following drawing conventions are followed.

Every representation of a single compound (this implies also salts, defined mixtures, etc.) is suitable for generation of InChI. Below is a short list of examples to show the capabilities of InchI key. Given is the structure drawing with the corresponding standard InChI key.

Example: glycin


Example: nitro-compound


Example: sodium chloride


Example: tautomeres heteroaromatic compound


Not suitable for InChI

The examples below show some areas which are problematic for InChI and are not supported.

a) InChI cannot recognize stereochemistry implied in a pseudo-3D drawing such as the chair conformation of a six-member ring.


b) InChI can only process compounds with fully defined constitution.


c) InchI may have problems with organometallic compounds such as Grignard compounds. The first 2 representations are OK, but the third generates a different InChI key.


Problematic is this representation, but it is not drawn with common chemical sense.


For more information on Mol files and InChI Keys click here.