  A dielectric model of electrostatic solvation is applied to describe
potentials of mean force in water along reaction paths for: a) formation of a
sodium chloride ion pair; b) the symmetric SN2 exchange of chloride in
methylchloride; and c) nucleophilic attack of formaldehyde by hydroxide anion.
For these cases simulation and XRISM results are available for comparison. The
accuracy of model predictions varies from spectacular to mediocre. It is argued
that: a) dielectric models are physical models, even though simplistic and
empirical; b) their successes suggest that second-order perturbation theory is
a physically sound description of free energies of electrostatic solvation; and
c) the most serious deficiency of the dielectric models lies in the definition
of cavity volumes. Second-order perturbation theory should therefore be used to
refine the dielectric models. These dielectric models make no attempt to assess
the role of packing effects but for solvation of classical electrostatic
interactions the dielectric models sometimes perform as well as the more
detailed XRISM theory.
