Monte Carlo simulation with statistical perturbation theory is used to study the solvent effects on the relative free energies of solvation and the difference of partition coefficients (DeltalogP) for Cl- to F-mutation in diverse solvents. Comparison of relative free energies for mutation of Cl- to F-, in H2O (TIP3P) is made with the experimental work. There is a good agreement between two studies. There is also good agreement between the calculated structural properties of this study and the published and experimental results. For ion pairs, the solvent Born's function and the differences in solvent-ion interaction dominate the differences in the relative free energies of solvation and the difference of partition coefficients. (C) 2002 Published by Elsevier Science B.V.