Intermediate structures are often used to describe reaction mechanisms such as in textbook presentations of a nucleophile substitution: Similar to these intermediate structures of a reaction mechanism there are Imaginary Transition Structures (ITS) or Condensed Graphs of Reaction (CGR) , that conceptualize a chemical reaction as one single pseudo molecule with incoming bonds and outgoing bonds. Delannée and Nicklaus have used this idea to create a novel reaction representation "ReactionCode" , which is a hierarchical code beginning from the reaction center and then continuing out from there. These presentations of reactions are alternatives to the arrow notation and have lots of benefits . The arrow notation will probably never disappear in favor of reaction graph models, but since they are interconvertible and are very similar to reaction mechanism descriptions, Reaction SPL provides a framework for these different conceptualizations to coexist. This point has been made already in our enzymatic reaction description. But now we generalize this for use with any molecular structures, no matter how large or small, polymeric, template-driven or random.