With the validated reference electronic structure method, we followed the intrinsic reaction path from the transition state to the reactant and the enolate as shown in Figure We hypothesized that this anomalous behavior comes from not considering structures with stretched C-H bonds in the original fitting process of the 3OB-3-1 parameter set derivation. To elucidate the origin of the total potential energy provided by the repulsive potential C-C and C-H pair atoms for the reactants and TS in Figures and. This comparison allowed us to determine which distance intervals are more frequently occupied at the TS compared to the reactants. As the reaction progresses to the transition state, the NADPH ring moves closer to the substrate to transfer the hydride from C 4 to C β (see Figure ).