Assigning the stereochemical configuration of a cyclophane or a metallocene is a rare task out there for most chemists. Two classes of molecules, cyclophanes and metallocenes, have flat features that can be tough to assign priority numbers to.

I ran into an organic chemistry resource on LinkedIn that was worth zooming in on. It is a blog called MakingMolecules and it features graphics that give instruction and illustrate most aspects of sophomore organic chemistry. Having taught organic chemistry I know that nomenclature is a favorite topic among students (wink wink, nod nod), especially where stereochemical configurations are concerned. Ah …, if only the world had only chiral acyclic hydrocarbons to name. As we know, there is much, much more than that.

Finding a chiral carbon atom on most simple molecules isn’t that hard. Find a carbon atom with 4 different groups attached and then check for symmetry around it from every direction while you rotate the parts.

If it has rotational symmetry or a plane of symmetry including the atom of interest, then it may not be a chiral “center”. Molecules with a C₂ symmetry axis but without a mirror plane can be chiral.

The more difficult molecules to characterize as chiral are those that have unusual rules necessary for an R or S configuration.