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

Glycin InChi 

Example: nitro-compound

Nitro Compound InChi 

Example: sodium chloride

Sodium Chloride InChi 

Example: tautomeres heteroaromatic compound

Tautomeres Heteroaromatic Compound InChi 

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.

Unsuitable InChi 

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

Unsuitable InChi 

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.

Unsuitable InChi 

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

Problematic InChi

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