For a number of functional groups, the group electronegativity and hardness in the gas phase and in different solvents was calculated using the recently introduced self-consistent isodensity polarized continuum model (SCI-PCM). The results indicate that the groups become less electronegative and less hard with increasing dielectric constant. Using the calculated functional group properties and Sanderson's electronegativity equalization principle, charge distributions in the alkyl alcohols X−OH and their conjugated bases XO- (with X = −CH3, −CH2CH3, and −CH(CH3)2 are determined in solution. The calculated charge distributions are used in a study of the inversion of alkyl alcohol acidity from gas phase to aqueous solution. Relative acidities are calculated in the gas phase and in aqueous solution for methanol, ethanol, 2-propanol and tert-butanol. The experimentally observed inversion of the acidity sequences of these systems is reproduced, and special importance is assigned to the stabilization energy of the conjugate bases in both media.

The SN2 reactions X- + CH3Y → Y- + CH3X have been investigated in the gas phase and in solution using the Hartree−Fock level with 6-31+G* and 3-21G* bases, respectively. In the gas phase the interpretation has been done in the context of the HSAB principle using Gázquez's formalism using the polarizability (proportional to softness) of the two minima corresponding to the two ion−molecule complexes, and the TS, the softness of the nucleophile and the charge on the leaving group. The thermodynamic study shows that the reaction energy, ΔE r - p and the energy differences between the two ion−molecule complexes, ΔE m, are close to the experimental data available. The application of the MHP indicates that in these reactions the molecules arrange themselves to be as hard as possible. The polarizable continuum model (PCM) has been used to study the influence of the solvent on the kinetics of the SN2 reaction. The application of Gázquez's formula provides fundamental information in a case study, with X = Cl and Y = I:  the activation energy calculated with the PCM model yields a very good correlation with the values obtained with Gázquez's formula. Finally, we concentrate on the influence of solvation on the nucleophilicity and the kinetics using the (PCM) model with X = F, I and Y = Br and compare the results with the gas phase. The order of reactivity in the gas phase is F- > I-, which is the same order as in the solvent using the polarizable continuum model, but opposed to experiment. If, however, we take into consideration the interaction energy caused by the hydrogen bond, the order of reactivity in solution is reversed yielding the same results as experiment.

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The effective fragment potential (EFP) model has been used to study the effect of adding increasing numbers of the water molecules on several DFT-based reactivity descriptors of NH 3 . The HOMO-LUMO gap and electrophilic hardness are seen to increase with addition of water molecules. The importance on the wave function relaxation in the solvent effect on ammonia's properties is shown when analyzing the relaxation part in the electrophilic hardness and condensed Fukui function for the nitrogen atom. An increase in the atomic softness for the nitrogen atom with decreasing the global softness is observed. The saturation point for solvatation of ammonia was located around a cluster with 16 molecules of water. Atomic properties such as the Mulliken population, condensed Fukui function, and atomic softness for nitrogen and electrophilic global properties such as the hardness and its components for dilute solutions are predicted faithfully.

The effect of solvent on the electronegativity, hardness, and condensed Fukui function, and atomic softness for a set of diatomic and small polyatomic molecules and ions has been studied using the effective fragment potential (EFP) model. The binding function was used for monitoring the solvation of the molecule. We do not observe a decrease in the HOMO-LUMO gap in the solvent. All anions show a significant change in the chemical potential. Both HOMO and LUMO energy levels decrease in the solvent phase as compared to the gas phase. For the major part of the acids, the increase in the LUMO orbital energy is larger than in the HOMO orbital energy. For the group of salts, we observe an increase in the LUMO energy level and a similar decrease in the HOMO energy level, resulting in a small change in the chemical potential. The importance of the change in the wave function upon solvation was shown through an analysis of the relaxation part in the hardness and condensed Fukui function. Very close values found for the same ions in molecules such as LiH, LiF, NaH, NaF, and LiF indicate that in these cases very good separated ion pairs are present.