[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]]
         Class nitrogen ylides [RmN+-CR2]
           Class azomethine ylides [R2C=N(R)+-CR2 <-> R2C-+N(R)=CR2]