PubChem provides property information on the biological activities of small molecules. A service of the National Institute of Health.

Part of the TOXNET system, ChemIDplus monitors over 70 chemical resources and provides access to them for identifying more than 380,000 chemicals cited in NLM databases. Information includes synonyms, formulas, toxicity, properties and structure.

A chemistry search engine that aggregates and indexes chemical structures and their associated information into a single searchable repository. Search by chemical name, structure, CAS registry #, InChI, SMILES and properties.

Sigma-Aldrich is a chemical product supplier. Their website also offers several chemical search options: search by substructure, calculate molecular weight, search for a chemical to find properties, safety information, references, reagents, and much more