PubChem

PubChem is a collection of freely accessible chemical information. It is managed by the U.S. National Institutes of Health. PubChem records are contributed by hundreds of data sources, including government agencies, chemical vendors, journal publishers, and more. PubChem mostly contains small molecules, but it also includes larger molecules such as nucleotides, carbohydrates, lipids, peptides, and chemically-modified macromolecules. It also includes drug information.

PubChem allows you to search chemicals by name, molecular formula, structure, and other identifiers. You can use it to study chemical and physical properties, biological activities, safety and toxicity information, patents, literature citations and more.