Woodward and Hoffmann developed the orbital symmetry conservation concept further over the following years into the Woodward-Hoffman rules to predict the stereospecificity in the whole new class of pericyclic reactions . The impact of their findings for the wide adoption of concepts from theoretical chemistry into the thinking of organic chemists in the following decades is profound and cannot be overstated. However, the Woodward-Hoffmann rules are also a product of the limited knowledge and computational power available in the 1960s, when quantum chemistry was in its infancy. Therefore, they focus strongly on the equilibrium structures of the reactant and product and paint a rather static picture of these reactions with limited insight into their mechanisms. Additionally, their picture of the thermal reactions on the ground state potential energy surfaces (PES) is much clearer than for the photochemical reactions. It is, for example, unclear from the original formulation of the Woodward-Hoffmann rules how the ππ ground state electron configuration of the product, which is a doubly excited π * π * configuration at the reactant geometry, is achieved during the reaction, or which electronic state the reaction is taking place in.