A chemical directory can come in one of two different flavors, technical and commercial.
Technically Oriented Chemical Directories
This kind of chemical directory allows finding a chemical by its molecular formula, common name, or other technical specification. It is a directory for those with technical familiarity of chemicals.
Once you specify a name, formula etc. the directory takes you to a page that lists the chemicals meeting the search criteria. Against each, supplier names are also given. You can then get more details of a particular supplier, or a particular chemical.
Links would also be available for getting an offer from a particular supplier for a chemical.
Such a technically oriented chemical directories would typically have other technical features, such as chemical calculators that calculates different properties such as molecular mass from a formula or other information.
Another valuable technical feature is a property explorer that calculates drug-relevant properties from valid chemical structures. This helps identify high-risk side effects of the structure. You can identify toxicity for...