A classical potential-based framework for modeling mechanochemical reactivity via molecular distortion: demonstration for a Diels–Alder reaction

Abstract

Mechanochemical reactions are increasingly studied using molecular dynamics simulations to understand mechanically activated chemical transformations. However, accurately capturing reactivity under mechanochemical conditions using classical potentials remains a challenge because standard models inhibit force-induced distortion of reactant species. In this study, we used the REACTER protocol, a method for simulating reactive events via dynamic bond changes, with a classical potential modified to allow the molecular distortion observed in first-principles calculations of a 4 + 2 Diels–Alder cycloaddition reaction. The approach was used to simulate the reaction in non-mechanochemical conditions with a solvent and no external stress, as well as in mechanochemical conditions. Mechanochemical simulations were run at hydrostatic stresses of 0.1 MPa and 2.5 GPa, both with and without shear applied, to investigate how the stress state influences reactivity. Relative to the non-mechanochemical reference case, hydrostatic stress and shear stress increased reaction yield. This increase was due to molecular distortion, the primary mechanism by which mechanical force activates chemical reactions, that could only be modeled using the modified classical potential. However, some of the increase in reaction yield was attributable to secondary mechanochemical activation mechanisms. Specifically, hydrostatic stress decreased the distance between reactants and shear stress facilitated alignment of reactants in the direction of imposed shear. This work provides new insight into how the stress state affects mechanochemical reaction mechanisms and establishes a generally applicable framework for improving classical potential-based simulations for organic reactions.