The Effect of Microsolvation on E2 and SN2 Reactions: Theoretical Study of the Model System F− + C2H5F + nHF

The model reaction system F− +C2H5F + nHF (n = 0–4) has been investigated by use of a density‐functional method, in order to achieve a qualitative understanding of the effect of solvation on the E2 and SN2 reactions. Two characteristic effects already occur upon monosolvation: a) the activation energies of the E2 and SN2 pathways increase significantly and even become positive, because reactants are more strongly solvated than transition states; b) the SN2 transition state is stabilized much more and becomes lower in energy than the anti‐E2 transition state. This agrees with general experience from gas‐ and condensed‐phase experiments. The solvation is analyzed from two complementary viewpoints: a) as an interaction between solvent molecules and the F−/C2H5F reaction system; b) as an interaction between the [F−, nHF] solvated base and the C2H5F substrate. The extent to which condensed‐phase characteristics can be modeled by this microsolvation approach is discussed.