Hydrogen transfer reaction: Bond formation and bond cleavage through the eyes of interacting quantum atoms

Hydrogen transfer from hydroquinone to the methoxy radical was studied using the density functional theory. The energy decomposition technique, interacting quantum atoms, was employed for a detailed investigation of the changes that the bonds of interest go through along the minimum energy path in the vicinity of the transition state. The whole system was divided either into two or three fragments. The two-fragment analysis enabled investigation of the bond that is formed or the one that is cleaved by defining the fragments as reactants and as products, respectively. The three-fragment analysis (the fragments being semiquinone, hydrogen atom and methoxy radical) was used for the simultaneous analysis of the two phenomena, bond cleavage and bond formation. Additionally, it enabled the interaction between the particle that donates the hydrogen atom and the one that accepts it to be investigated. This interaction is characterized by attractive non-classical and repulsive classical interactions. It was demonstrated that the transferring hydrogen atom undergoes the most pronounced energy changes and gives the largest contribution to the deformation energy.