We present a parametrization of the SM5.4 solvation model, previously
applied to aqueous solutions and general organic solvents, for predict
ing free energies of solvation in chloroform. As in all SM5 models, th
e calculations are based on a set of geometry-based functional forms f
or parametrizing atomic surface tensions of organic solutes. In partic
ular, the atomic surface tensions depend in some cases on distances to
nearby atoms. Combining the atomic surface tensions with electrostati
c effects included in a Fock operator by the generalized Born model en
ables one to calculate free energies of solvation by a quantum mechani
cal self-consistent reaction field method. Atomic charges are obtained
by both the AM1-CM1A and PM3-CM1P class IV charge models, which yield
similar results, and hence the same atomic radii and similar surface
tension coefficients are used with both charge models. Experimental fr
ee energies of solvation and free energies of transfer from aqueous so
lution are used to parametrize the theory for chloroform. The parametr
ization is based on a set of 205 neutral solutes containing H, C, N, O
, F, S, Cl, Br, and I that we used previously to parameterize a model
for general organic solvents plus 32 additional solutes added for this
study. For the present parameterization, we used free energies of sol
vation in chloroform for 88 solutes, free energies of solvation in oth
er solvents for 123 solutes, and free energies of transfer from water
to chloroform for 26 other solutes. We obtained a mean unsigned error
in the free energies of solvation in chloroform of 0.43 kcal/mol using
CM1A atomic charges and 0.34 kcal/mol using CM1P atomic charges.