As shown in Fig. , the disrotatory, thermally allowed ground-state minimum energy path (MEP, blue line) goes through a transition state (TS), verified to be a first-order saddle point, to reach the primary ring-opening product cZc-1,3,5-hexatriene (cZc-HT). On the other hand, the conrotatory, photochemically allowed ground-state MEP (orange line), travels uphill onto a much higher barrier TS than the disrotatory MEP. Furthermore, the minimum energy CI (MECI) between the ground and first excited state in the vicinity of the pericyclic minimum in the π * π * state is both geometrically (see the similarities in the structures of MECIcon and TScon in Fig. ) and energetically (Fig. ) close to the conrotatory TS. The MECIcon is energetically much closer to the Franck-Condon region of the ππ * state than to the reactant ground state minimum. Thus, it can be assumed that its presence is the main reason for the significantly higher barrier and different topology for the conrotatory pathway on the ground state PES compared to the disrotatory pathway. The higher barrier of course makes the conrotatory pathway less favorable compared to the disrotatory one. Additionally, the close proximity of the conical intersection implies that nonadiabatic crossing could prevent the molecule from reacting even if it were to find its way to the conrotatory path. This has been called "up-funnelling" and "diabatic trapping" in previous photochemical studies. Hence, the CI can be regarded as an important contributor to the forbidden nature of the thermal conrotatory reaction.