MolDraw › Chemistry tools › Chemical Identifier Converter
Chemical Identifier Converter
In short: Paste any one identifier: SMILES, InChI, InChIKey, a MOL block, a PubChem CID or a name. You get all of them at once: canonical SMILES with and without stereo, standard InChI and InChIKey, molecular formula, molar mass, exact mass and a V2000 MOL file, each with a copy button.
CC(=O)Oc1ccccc1C(=O)O → InChIKey BSYNRYMUTXBXSQ-UHFFFAOYSA-N, C9H8O4, 180.159 g/mol, exact mass 180.0423 Da. Caffeine is RYYVLZVUVIJVGH-UHFFFAOYSA-N.Examples:
How to use the identifier converter
- Paste a SMILES, InChI, InChIKey, MOL block, PubChem CID or compound name, or open a .mol file. The type is detected automatically.
- Press Convert. SMILES and MOL input are read in your browser; names, InChIKeys and CIDs are looked up in PubChem.
- Read every identifier in the table. The small grey text under each name says where the value came from.
- Press Copy next to any value, Copy all, or Download .mol for the V2000 MOL file.
The identifiers in the table
| Identifier | What it is | How this page gets it |
|---|---|---|
| Canonical SMILES (isomeric) | One line of text with atoms, bonds, rings, charges and stereo. Canonical means the same molecule always gives the same string with one program. | Computed in your browser with OpenChemLib. Other programs (RDKit, PubChem) write a different but equivalent canonical string. |
| Canonical SMILES (no stereo) | The same without @, @@, / and \. | Computed in your browser. |
| Standard InChI | The IUPAC identifier, built in layers: formula, connections (/c), hydrogens (/h), charge (/q, /p), stereo (/b, /t, /m, /s) and isotopes (/i). | From PubChem for SMILES and MOL input (NCI resolver if PubChem has no record). |
| Standard InChIKey | A 27-character hash of the InChI for web and database search: 14 letters for the connectivity, 8 for stereo and isotopes, SA for standard version 1, and one letter for protonation (N = neutral). | Computed in your browser from the InChI (SHA-256, same algorithm as the InChI software) and checked against PubChem. |
| Molecular formula, molar mass, exact mass | Hill formula; average molar mass from standard atomic weights; monoisotopic mass from the most abundant isotopes. | Computed in your browser. |
| MOL file (V2000) | Atom block with 2D coordinates and a bond block, readable by almost every chemistry program. | Computed in your browser. Your own coordinates are kept for MOL input; otherwise a 2D layout is made. |
Known values to check against
| Compound | InChIKey |
|---|---|
| Aspirin | BSYNRYMUTXBXSQ-UHFFFAOYSA-N |
| Caffeine | RYYVLZVUVIJVGH-UHFFFAOYSA-N |
| L-Alanine | QNAYBMKLOCPYGJ-REOHCLBHSA-N |
| Ethanol | LFQSCWFLJHTTHZ-UHFFFAOYSA-N |
Limitations
- The standard InChI is not generated in your browser. It is looked up in PubChem (or the NCI resolver), so InChI output, and any name, InChIKey or CID input, needs an internet connection. SMILES, MOL files, formula and masses work offline.
- PubChem standardises structures. For some inputs (tautomers, charged forms, salts) the record it returns is not exactly what you typed; the page compares the two and warns you when they differ.
- A name is resolved to the first PubChem record that matches it. Trade names and abbreviations can be ambiguous.
- MOL files with chiral flag 0 are read with the stereocentres as drawn (absolute), like most software. If you meant relative stereo, the InChI will still list it as absolute.
- Only standard InChI (InChI=1S/) is turned into an InChIKey here. Non-standard InChIs are not.
Have a structure drawing instead? Draw it in MolDraw, the free online chemical structure editor, copy its SMILES and paste it here.
Open MolDraw editorFrequently asked questions
How do I convert SMILES to InChI and InChIKey?
Paste the SMILES and press Convert. The canonical SMILES, formula and masses are computed in your browser, and the standard InChI is looked up in PubChem. Aspirin, CC(=O)Oc1ccccc1C(=O)O, gives InChI=1S/C9H8O4/c1-6(10)13-8-5-3-2-4-7(8)9(11)12/h2-5H,1H3,(H,11,12) and the InChIKey BSYNRYMUTXBXSQ-UHFFFAOYSA-N.
Can I convert an InChIKey back to a structure?
Only by looking it up. An InChIKey is a hash, so the structure cannot be calculated from it. The converter searches PubChem for the key and, if a compound is found, gives its SMILES, InChI and MOL file. For example LFQSCWFLJHTTHZ-UHFFFAOYSA-N returns ethanol.
Is the InChIKey computed in the browser?
From an InChI, yes. The InChIKey is a SHA-256 hash of the InChI string, and this page computes it exactly like the IUPAC InChI software. The InChI itself cannot be made in the browser here; for SMILES and MOL input it comes from PubChem (or the NCI resolver for structures PubChem does not have).
What is the difference between isomeric and non-isomeric SMILES?
Isomeric SMILES keep stereochemistry (@ and @@ for stereocentres, / and \ for double bonds) and isotopes. Non-isomeric SMILES drop them, so L- and D-alanine give the same string (CC(C(O)=O)N with this converter). Use isomeric SMILES when stereochemistry matters.
Why does the InChIKey of L-alanine differ from that of alanine?
The first 14 letters encode connectivity and are the same (QNAYBMKLOCPYGJ). The next block encodes stereochemistry: L-alanine is QNAYBMKLOCPYGJ-REOHCLBHSA-N, while alanine without defined stereo is QNAYBMKLOCPYGJ-UHFFFAOYSA-N.
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