Chemical reaction with two different elementary transition states

The phenomenon of the elementary chemical reaction with two different transition states (TSs) between reactant and product is represented. Different examples of the reaction with two transition states were reported during the last decade. In some cases, one route is dominant, in another cases the energy of the barriers is similar, but the electronic structure of TSs are different. The Valence Bond (VB) approach provides the rationalization for the phenomenon of the chemical reaction with two TSs: the reactant and product pair is based on three dominant VB structures (anchors). The VB approach provides an opportunity to distinguish between different resonance mechanisms - different TSs. The 2D-domain is based on two minima, the reactant and the product, which are connected by two different TSs and can include the electronic degeneracy. Physical consequences of the chemical reaction with dual reaction routes are discussed.