Can a chemical compound be claimed by its characteristics instead of its structure?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

Yes, chemical compounds can be claimed by their characteristics when the structure is unknown. The MPEP 2173.05(t) provides this option:

“A compound of unknown structure may be claimed by a combination of physical and chemical characteristics.”

This approach is supported by legal precedent, such as Ex parte Brian. When structural information is unavailable or incomplete, describing a compound by its physical and chemical properties can be an effective way to claim it in a patent application. This method allows inventors to protect their discoveries even when full structural elucidation is not possible or practical.