In the conrotatory case, the preserved symmetry element is a C2 rotation axis in the ring plane (see a visualization together with the schematic of the HOMO in Fig. ). This results in correlation of the reactant HOMO with the lowest unoccupied molecular orbital (LUMO) of the product and vice versa. In an electronic state picture, the reactant ground state (ππ) Slater determinant correlates with the Slater determinant of a doubly excited (π * π * ) state in the product, which is energetically unfavorable and leads to a transition state of much higher energy than the transition state of the disrotatory reaction. Therefore, the conrotatory pathway is labeled thermally "forbidden".