Steering Diels-Alder Reaction with Mechanical Force: Structure Deformation versus Electron Rearrangement

Mechanochemistry presents a sustainable alternative to the conventional solvothermal method. The mechanism by which force remodels the reaction microenvironment (RME) to regulate reactivity remains poorly understood. In this study, density functional theory (DFT) calculations are utilized to systematically examine the force-applied Diels-Alder (DA) reaction between surface-anchored anthracene and methyl acrylate. It is found that force-induced deformation of molecular structure and rearrangement of electrons provide a synergistic effect on the reaction. The results indicate that the reaction barrier declines when the force is applied toward the dienophile, while it rises when the force is applied in the opposite direction. Activation strain analysis reveals that this force-induced barrier modulation is dominated by the strain energy accumulation in the deformation of molecular structure. For reaction-promoted force, the reactant complex exhibits a stronger energetic response to mechanical deformation than the transition state (TS), which reduces the reaction barrier. Structural analysis further validates that reaction-promoted force triggers an asymmetric response of the two forming C-C bonds, driving the reaction from a synchronous to an asynchronous mechanism. The force-induced deformation of the molecular structure is accompanied by a reduction of the frontier orbital energy gap and a force-dependent reorganization of intermolecular electron transfer. The electron transfer is promoted unidirectionally from the diene to the dienophile. These results provide important insights into force-controlled reactions.