Search for chemical compounds by structure or substructure — drawing a molecule and finding matching compounds, suppliers and data. Below are the main free databases that support structure and substructure search.
Where to search by structure
- PubChem — NCBI’s free chemical database; draw a structure or paste SMILES/InChI and run identity, similarity or substructure searches across millions of compounds.
- ChemSpider — the Royal Society of Chemistry’s structure-searchable database with links to literature and suppliers.
- Sigma-Aldrich / Merck — substructure search of catalogue reagents for ordering.
How structure search works
Draw the molecule (or enter a SMILES or InChI string) and choose the search type: exact (the same compound), substructure (compounds containing your fragment), or similarity (related structures by a similarity threshold). PubChem is the best free starting point.
Frequently asked questions
How do I search for a compound by structure?
Use PubChem or ChemSpider: draw the structure or enter SMILES/InChI and run an exact, substructure or similarity search.
What is a SMILES string?
A text notation that encodes a molecule’s structure (e.g. CCO for ethanol), accepted by most structure-search tools.
