Real-Space Approach to the Reaction Force: Understanding the Origin of Synchronicity/Nonsynchronicity in Multibond Chemical Reactions

In this article, we present a complementary analysis based on the reaction force F(xi)/reaction force constant kappa(xi) and noncovalent interactions (NCI) index to characterize the energetics (kinetic and thermodynamics) and mechanistic pathways of two sets of multibond chemical reactions, namely, two double-proton transfer and two Diels-Alder cycloaddition reactions. This approach offers a very straightforward and useful way to delve into a deeper understanding of this type of process. While F(xi) allows the partition of the whole pathway into three regions or phases, kappa(xi) describes how orchestrated are the bond-breaking and bondformation events. In turn, NCI indicates how the inter- and intramolecular bonds evolve. The most innovative aspect is the inclusion of the formation of the reactant complex along the pathway, which, by means of NCI, unveils the early molecular recognition and the comprehension of its role in determining the degree of the synchronicity/nonsynchronicity of one-step processes. This approach should be a useful and alternative tool to characterize the energetics and the mechanism of general chemical reactions.