Inspection of the DFT-modelled species reveals that bondstretching vibrational modes (e.g., the single imaginary vibrational frequency for species 7a and two imaginary vibrational frequency for species 8a) distort their respective geometries along the MEPs and towards their reaction-graph adjacent species. A directed graph that encodes this information is shown in Fig. following the approach described for stereoisomerism. Self-loops are required to account for both displacement directions of a vibration and here describe the steep walls of the PES. By assigning energies to each reaction graph vertex and transformational information (energy gradients and curvatures, and vibrational modes) to the graph edges, the resulting mathematical object as interpreted through the lens of TST is a compact encoding of the PES (Fig. ). The two PESs shown in Fig. have been calculated following this approach using interpolation and are isomorphic with the real-space PES shown in Fig. . While the reaction graphs produced within the formalism are based on the discrete and abstract nature of atom connectivity and hence do not represent geometric coordinates, their isomorphism with real-space PESs demonstrates a direct relationship to the underlying geometric coordinates. This capacity to give structure to multidimensional TST becomes important and powerful as the complexity of the chemical system increases as is demonstrated in the following Sections.