For concerted reactions where (at least) two atom connections form/break simultaneously such is the case for cycloadditions and chelotropic reactions, the list of atom-connectivity configuration species generated by the Polytope Formalism of constitutional isomerism does not differentiate between the cyclized species and the TS of its formation. An illustrative example is given in Fig. which shows the Diels-Alder reaction of [butadiene + ethene] 38a, to give cyclohexene 39a, via the TS 39aʹ. The corresponding atom-connectivity picture of these three species are as shown in Fig. . Both 39aʹ (TSκ1:κ4) and 39 (LMκ1:κ4) have the same atom-connectivities. A consequence of this is that the formalism under-samples the PES from the perspective of defining the important species involved. This is not a fatal limitation as knowing of it allows one to look for those additional species of the same configuration but different PES character. For example, when generating initial representative structures, the bonds (atom connections) in question can be constrained by either bond order or an appropriate bond length.