The NIST Chemistry WebBook provides users with easy access to chemical and physical property data for chemical species. From the National Institute of Standards and Technology (NIST), an agency of the U. S. Commerce Department.
Set of databases from the National Institute of Standards and Technology (NIST). Includes Physical Constants, Atomic Spectroscopy Data, Molecular Spectroscopy Data, Atomic and Molecular Data, X-Ray and Gamma-Ray Data, and more.
ChemSpider is a free collection of compound data from across the web, provided for the benefit of the community by the Royal Society of Chemistry (RSC). It aggregates chemical structures and their associated information into a single searchable repository.
ChemSynthesis is a freely accessible database of chemicals. This website contains substances with their synthesis references and physical properties such as melting point, boiling point and density.