International Chemical Identifier - InChIKey

InChIKey

The condensed, 27 character standard InChIKey is a hashed version of the full standard InChI (using the SHA-256 algorithm), designed to allow for easy web searches of chemical compounds. Most chemical structures on the Web up to 2007 have been represented as GIF files, which are not searchable for chemical content. The full InChI turned out to be too lengthy for easy searching, and therefore the InChIKey was developed. There is a very small, but finite chance of two different molecules having the same InChIKey, but the probability for duplication of only the first 14 characters has been estimated as only one duplication in 75 databases each containing one billion unique structures. With all databases currently having below 50 million structures, such duplication appears unlikely at present.

InChIKeys consist of 14 characters resulting from a hash of the connectivity information of the InChI, followed by a hyphen, followed by 9 characters resulting from a hash of the remaining layers of the InChI, followed by a single character indicating the version of InChI used, another hyphen, followed by single checksum character.

Example: Morphine has the structure shown on right. The standard InChI for morphine is and the standard InChIKey for morphine is BQJCRHHNABKAKU-KBQPJGBKSA-N.