Freely available chemical database.

Produced by National Center for Biotechnology Information (NCBI), which is part of National Library of Medicine - component of National Institutes of Health (NIH) in USA. Is linked with PubMed database.
PubChem includes substance information, compound structures and BioActivity data in three primary databases:

• Compound - contains more than 26 million unique structures
• Substance - contains more than 69 million records (chemical structures, synonyms, registration IDs, description etc.)
• BioAssay - contains BioActivity screens of chemical substances

More info, help etc. https://pubchemdocs.ncbi.nlm.nih.gov/about