A HIERARCHICAL-CLASSIFICATION SCHEME FOR CHEMICAL-REACTIONS

Several known approaches to classification of structural changes in th e course of chemical reactions are briefly discussed. The hierarchical five-level classification scheme is suggested for organic interconver sions in which the bond redistributions (summarizing all required step s of the reaction process) are exactly known. The main hierarchy level s, i.e., reaction category, reaction class, interconversion type, topo logical type, and reaction type-and also corresponding sublevels-are i llustrated by numerous examples. The first two levels together with re action subcategories and subclasses relate to the nature of educt and product species (neutral or dipolar molecules, ions, radicals, etc.) a nd to contours and graphs formed by bonds which change their multiplic ity during the reaction. The interconversion, topological, and reactio n types are uniquely characterized by classification, symbolic, and sk eletal equations, respectively; the subtypes are also associated with specific kinds of equations. The central hierarchy attribute, i.e., cl assification equation, is shown to closely correspond to what organic chemists typically use in order to systematize simple processes with c yclic and linear electron transfers. Finally, the application of the s uggested classification scheme to construction of hierarchically organ ized codes for organic reactions is finally demonstrated in the paper.