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
                 1.1.1 Class alkanes [CnH2n+2] - saturated acyclic hydrocarbons
                 1.1.2 Class cycloalkanes - saturated monocyclic hydrocarbons (with or without side chains)
                 1.2 Class olefins
                 1.3 Class acetylenes
                 2.1.12.4 Class arenes - monocyclic and polycyclic aromatic hydrocarbons
                 2.1.21.1 Class cumulenes [R2C[=C]nR2 (n≥3)]
                 2.1.21.2 Class acenes - polycyclic aromatic hydrocarbons consisting of fused benzene rings in a rectilinear arrangement
                 2.2.3.1.2 Class annulenes [CnHn (n=even) or CnHn+1 (n=odd)]