Digging on the mechanism of some Diels–Alder reactions: the role of the reaction electronic flux

Within the framework of the reaction force analysis, numerical data obtained from DFT calculations were used to characterize the mechanism of three Diels–Alder reactions involving three substituted furandione as dienophile, and a chiral anthracene, as diene. Then, the Marcus potential energy function and the activation strain model were used to rationalize the energetics of the reactions and to obtain physical insights on the nature of activation energies. It has been found that the activation processes are dominated by structural arrangements of reactants, basically due to the approach of the diene to the dienophile to start the reaction. Besides, the electronic activity taking place along the reaction coordinate have been analyzed through the reaction electronic flux. It has been found that the electronic activity that emerge more intensively within the transition-state region, is mainly due to electronic transfer effects, due to the breaking and forming π bonds. Although polarization effects are also present but to a lesser extent.