Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         "crystal-kingdom"
           chemical substances
             reactive intermediates
               Class dipolar compounds
                 Class ylides [[RmX+-YRn [<-> RmX=YRn] (X=N,O,P,S,etc.; Y=C, etc.)] or [Z=X+-YRn <-> Z-+X=YRn] or [RmX+-Y <-> RmX=Y]]
                   1.1 Class nitrogen ylides [RmN+-CR2]
                   1.2 Class oxygen ylides [RmO+-CR2]
                   1.3 Class phosphorus ylides [RmP+-CR2 <-> RmP=CR2]
                   1.4 Class sulfur ylides [RmS+-CR2 <-> RmS=CR2]
                   1.5 Class arsenic ylides [RmAs+-CR2 <-> RmAs=CR2]
                   2.1.1 Class amine imides [R3N+-NR]
                   2.1.2 Class nitrile imides [RC≡N+-NR <-> RC+=NN-R <-> RC-=+N=NR]
                   2.2.1 Class amine oxides [R3N+-O]
                   2.2.2 Class nitrones [R2C=N+(O-)R' (R'≠H)]
                   2.2.3 Class nitrile oxides [RC≡N+-O <-> RC-=+N=O]
                   2.3 Class nitrile sulfides [RC≡N+-S <-> RC-=+N=S]
                   3 Class betaines