[chemical substances]
   reactive intermediates
     Class cations [X+]
       Class onium compounds
         1.1.1 ammonium [H4N+]
         1.1.2 Class nitrilium ions [RC≡NH+]
         1.2 phosphonium [H4P+]
         1.3 arsonium [H4As+]
         1.4 stibonium [H4Sb+]
         1.5 bismuthonium [H4Bi+]
         2.1 Class oxonium ions [R3O+]
         2.2 sulfonium [H3S+]
         2.3 selenonium [H3Se+]
         2.4 telluronium [H3Te+]
         3 Class halonium ions [R2X+ (X=halogen)]