Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         "crystal-kingdom"
           chemical substances
             chemical compounds
               Class hydrocarbons [CxHy] - compounds consisting of carbon and hydrogen only
                 Class olefins
                   1.1 Class alkenes [CnH2n] - unsaturated acyclic hydrocarbons having one double bond
                   1.2 Class alkadienes - unsaturated acyclic hydrocarbons having two double bonds
                   1.3 Class alkatrienes - unsaturated acyclic hydrocarbons having three double bonds
                   2.1 Class cycloalkenes
                   2.2 Class cycloalkadienes
                   2.3 Class cycloalkatrienes