A Concept for a Generic Stereochemistry Descriptor

In organic chemistry, Cahn-Ingold-Prelog (CIP) rules and R and S descriptors are a well-established standard for identifying the stereochemistry of tetrahedral stereocenters. For other molecular geometries, such as the octahedral or bipyramidal geometries regularly observed in organometallic and molecular inorganic chemistry, there are point solutions for specific geometries and compounds classes but there is no systematic generally applicable solution. To overcome this limitation, a new generic stereochemistry descriptor is proposed. This stereodescriptor is independent of the type of molecular geometry (e.g., T-4, OC-6, TBPY-5) and is aimed to support any currently known molecular geometry. It does not require prior knowledge of the the type of molecular geometry, nor does it explicitly determine the molecular geometry. Several geometries and examples are discussed, including complex examples such as multi-substituted ferrocenes and octahedral 'enhanced' stereochemistry, and the new stereodescriptor is compared with the CIP rules. The new stereodescriptor can, for example, form the basis for a future extension of the International Chemical Identifier (InChI) to uneqivocally identify the stereochemistry of organometallics and molecular inorganics.