The PubChem Patent View page contains information on what chemicals are mentioned in a particular patent document. Below is an example of the patent view page (for U.S. Patent 5969156):
The Patent View page for a given patent provides compounds and substances mentioned in it, along with other information including patent title, abstracts, application and publication dates, applicant, and inventor. It also contains patent classification information based on World Intellectual Property Organization (WIPO)’s International Patent Classification (IPC). Currently, it does not support the Cooperative Patent Classification (CPC).
It is important to understand that the PubChem Patent View page currently does not present the context about why a particular chemical was mentioned in the patent. That is, it is not possible to tell if the chemical is indeed the subject matter of the patent grant, or if it is just mentioned as a part of prior arts in the background section.
Chemicals mentioned for a given patent are presented under the "Linked Chemicals" section, which has the "PubChem Compounds" and "PubChem Substances" subsections, as shown in the following Patent View page:
The "Patent Compounds" subsection displays the list of the unique chemical structures associated with the patent, while the "Patent Substances" provides information on who provided information on each chemical structure-patent association. The differences between "Compounds" and "Substances" in PubChem are explained in this document.
In general, a single invention may be described in multiple patent documents, including a patent application, patent grant, and reexamination certificate, and each of these documents is assigned to a patent identifier suffixed with a kind code (such as A1, A2, B1, B2, ...). And frequently, the same patent is filed in multiple national agencies. These are all separate patent documents in PubChem's system, but you can see which patent documents related this way by going to the patent family section: