FGROUP by class
Carbon Carbon skeleton Hydrocarbon ring N-heterocyclic O-heterocyclic S-heterocyclic Mixed-heterocyclic Oxygen Nitrogen Sulfur Acyl thioester (F540000) Thioester (F540000) Alpha-beta unsaturated acyl thioester (F540100) Phosphorus Halogen Boron Magnesium Silicon Iron Cobalt Asenic Selenium Tin