InChIKey (inchikey)

A hashed representation of the InChI.

The InChIKey is a fixed-length (27-character) condensed digital representation of an InChI, developed to make it easy to perform web searches for chemical structures.

An InChIKey consists of 14 characters (derived from the connectivity layer in the InChI), a hyphen, 9 characters (derived from the remaining layers), a character indicating the InChI version, a hyphen and a final checksum character. Contrast the InChI and InChIKey of the molecule represented by the SMILES string CC(=O)Cl:

obabel -:CC(=O)Cl -oinchi
InChI=1S/C2H3ClO/c1-2(3)4/h1H3

obabel -:CC(=O)Cl -oinchikey
WETWJCDKMRHUPV-UHFFFAOYSA-N

This is the same as using -oinchi -xK and can take the same options as the InChI format (see InChI format (inchi)):

obabel -:CC(=O)Cl -oinchi -xK
WETWJCDKMRHUPV-UHFFFAOYSA-N

Note that while a molecule with a particular InChI will always give the same InChIKey, the reverse is not true; there may exist more than one molecule which have different InChIs but yield the same InChIKey.

Note

This is a write-only format.