Unveiling the Mystery of Reaction Mechanisms

It can be hypothesized that chemical reactions take place through a sequence of events involving structural and electronic rearrangements; these events take the reactants into the products, thus achieving the chemical transformation. The ensemble of these events defines the mechanism of achemical reaction and its knowledge is very important since it may lead to control complexprocesses such as catalytic reactions which are a fundamental component of modern chemistry. In this presentation, we are going to review and discuss few concepts and methodologies that we havedeveloped to get insights into reaction mechanisms, special attention will be paid to the energies involved and to the electronic activity that is ultimately responsible for driving chemical reactions. The reaction force analysis (RFA) will be exposed as a quite useful tool to describe chemical events taking place within different regions along the reaction coordinate. These chemical events have been characterized as being of structural and/or electronic nature and they drive a chemical reaction in a cooperative way. Within this framework, structural and energetic characterization of transition states is a crucial issue to formulate reliable reaction mechanisms. On the other hand, the reaction electronic flux (REF) has proven to be a quite good and reliable descriptor of the electronic activity taking place during a chemical reaction. This activity is rationalized in terms of bond strengthening/formation and/or bond weakening/breaking processes and has been linked to the change of specific local electronic populations. To illustrate these ideas, we will use the combination of RFA and REF to analyze the mechanism of different kind of chemical reactions, going from simple isomerization reactions to complex catalytic transformations.