Dynamics of sterically hindered F- + i-C3H7Cl reaction: An enhancement of indirect mechanisms

It is essential but difficult to monitor the underlying atomistic mechanisms for the competitive nucleophilic substitution (SN2) and base-induced elimination (E2) reactions. Especially, the dynamic characters of bulky alkyl substitution halides remain unclear due to its complexity. Here, we present direct dynamics simulations of the fluoride anion reaction with isopropyl chloride, uncovering distinct dynamical behaviors compared to its ethyl chloride counterpart. Reaction dynamics simulation capture the key trends observed in differential scattering experiment, demonstrating predominant preference for the direct E2 pathway through stripping mechanisms at 1.9 eV of collision energy. Notably, an enhancement of indirect mechanisms emerges with increasing methyl substitution (from ethyl to isopropyl chloride), even at the high collision energy where such pathways are typically suppressed. This phenomenon arises from the synergistic effects of ion-induced dipole forces and van der Waals interactions between the reactants, coupled with the alkyl substitution-induced stabilization of the entrance-channel complex, which collectively prolong the interaction timescales. This work deepens an atomistic dynamics understanding of sterically hindered systems and highlights the role of the entrance channel on the chemical dynamics.