How Solvation Influences the SN2 versus E2 Competition [component]

unpublished
We have quantum chemically investigated how solvation influences the competition between the S N 2 and E2 pathways of the model F − + C 2 H 5 Cl reaction. The system is solvated in a stepwise manner by going from the gas phase, then via microsolvation of one to three explicit solvent molecules, then last to bulk solvation using relativistic density functional theory at (COSMO)-ZORA-OLYP/QZ4P. We explain how and why the mechanistic pathway of the system shifts from E2 in the gas phase to S N 2
more » ... on strong solvation of the Lewis base (i.e., nucleophile/ protophile). The E2 pathway is preferred under weak solvation of the system by dichloromethane, whereas a switch in reactivity from E2 to S N 2 is observed under strong solvation by water. Our activation strain and Kohn−Sham molecular orbital analyses reveal that solvation of the Lewis base has a significant impact on the strength of the Lewis base. We show how strong solvation furnishes a weaker Lewis base that is unable to overcome the high characteristic distortivity associated with the E2 pathway, and thus the S N 2 pathway becomes viable.
doi:10.1021/acs.joc.1c02354.s001 fatcat:urq3bn72wnfmtmucp2az3cr3j4