SMILES to InChIKey Converter
In short: Convert SMILES strings into searchable InChIKey identifiers. It is free, works in your web browser and needs no download.
Generate compact InChIKey identifiers from SMILES strings.
Input and output formats
| Input: SMILES | Output: InChIKey | |
|---|---|---|
| Full name | SMILES (Simplified Molecular Input Line Entry System) | InChIKey |
| What it holds | Atoms, bonds, rings, charges and stereo as one line of text. No coordinates. | A 27 character hash of the InChI, made for web and database search. It cannot be turned back into a structure without a lookup database. |
| File or form | .smi or plain text | Text like XXXXXXXXXXXXXX-YYYYYYYYYY-Z |
File Format Explained
SMILES is a compact text notation for molecular structure. It is useful for input, editing, and conversion workflows.
InChIKey is a fixed-length hashed identifier derived from an InChI. It is designed for fast database matching and web search, but it cannot be reversed perfectly without a database lookup.
Use InChIKey when you need a stable search key for a compound; use SMILES when you need an editable structure string.
Why use an InChIKey
InChIKeys are designed for searching. Pasting a full InChI or SMILES into a search engine often fails, because symbols such as =, /, and parentheses are treated specially. A 27-character key made only of letters and hyphens searches cleanly and matches database records reliably.
Example
Caffeine, CN1C=NC2=C1C(=O)N(C(=O)N2C)C, gives the InChIKey RYYVLZVUVIJVGH-UHFFFAOYSA-N. Searching that key returns pages for caffeine in PubChem, ChEMBL, and other databases.
Structure of the key
- First 14 characters: hash of the connectivity.
- Next 10 characters: hash of stereochemistry and isotope layers, plus version flags.
UHFFFAOYSAappears for structures with no stereo or isotope layers. - Last character: protonation (N = neutral).
FAQ
Do enantiomers get different keys? Yes, if the stereochemistry is defined in the SMILES. They share the first block and differ in the second. Can I get the structure back from a key? Only by database lookup, using InChIKey to SMILES.
Last updated: