pyrrole

pyroli puhekieltä Any of a class of aromatic heterocyclic compounds containing a ring of four carbon atoms and a nitrogen atom; especially the simplest one, C4H5N. (defdate)
1998, Georgina Ferry, Dorothy Hodgkin: A Life:

The way the red crystals absorbed light suggested that the molecule might contain a porphyrin-like structure, a flat ring made up of four smaller rings called pyrroles ….