FGROUP by class
Carbon Carbon skeleton Hydrocarbon ring N-heterocyclic Polycyclic Flavin (F223101) Carbazole (F223201) Porphine (F223301) Thiamine (F224101) O-heterocyclic S-heterocyclic Mixed-heterocyclic Oxygen Nitrogen Sulfur Phosphorus Halogen Boron Magnesium Silicon Iron Cobalt Asenic Selenium Tin