Absolute single-ion solvation free energy is a very useful property for understanding solution phase chemistry. The real solvation free energy of an ion depends on its interaction with the solvent molecules and on the net potential inside the solute cavity. The tetraphenyl arsonium-tetraphenyl borate (TATB) assumption as well as the cluster-continuum quasichemical theory (CC-QCT) approach for Li(+) solvation allows access to a solvation scale excluding the net potential. We have determined this free energy scale investigating the solvation of the lithium ion in water (H2O), acetonitrile (CH3CN) and dimethyl sulfoxide (DMSO) solvents via the CC-QCT approach. Our calculations at the MP2 and MP4 levels with basis sets up to the QZVPP+diff quality, and including solvation of the clusters and solvent molecules by the dielectric continuum SMD method, predict the solvation free energy of Li(+) as -116.1, -120.6 and -123.6 kcal mol(-1) in H2O, CH3CN and DMSO solvents, respectively (1 mol L(-1) standard state). These values are compatible with the solvation free energy of the proton of -253.4, -253.2 and -261.1 kcal mol(-1) in H2O, CH3CN and DMSO solvents, respectively. Deviations from the experimental TATB scale are only 1.3 kcal mol(-1) in H2O and 1.8 kcal mol(-1) in DMSO solvents. However, in the case of CH3CN, the deviation reaches a value of 9.2 kcal mol(-1). The present study suggests that the experimental TATB scale is inconsistent for CH3CN. A total of 125 values of the solvation free energy of ions in these three solvents were obtained. These new data should be useful for the development of theoretical solvation models.

Fluorinated organic molecules are playing an increased role in the area of pharmaceuticals and agrochemicals. This fact demands the development of efficient catalytic fluorination processes. In this paper, we have designed a new crown ether with four hydroxyl groups strategically positioned. The catalytic activity of this basic scaffold was investigated with high levels of electronic structure theory, such as the ONIOM approach combining MP4 and MP2 methods. On the basis of the calculations, this new structure is able to solubilize potassium fluoride in toluene solution much more efficiently than 18-crown-6 (18C6). In addition, the strong interaction of the new catalyst with the SN2 transition state leads to a very important catalytic effect, with a predicted free energy barrier of 23.3 kcal mol(-1) for potassium fluoride plus ethyl bromide reaction model. Compared with experimental data and previous theoretical studies, this new catalyst is 10(4) times more efficient than 18C6 for nucleophilic fluorination of alkyl halides. The catalysis is predicted to be selective, leading to 97% of fluorination and only 3% of elimination. Catalytic fluorination of the aromatic ring has also been investigated, and although the catalyst is less efficient in this case, our analysis has indicated further development of this strategy can lead to more efficient catalysis.

As propriedades estruturais, espectroscópicas e termodinâmicas de duas espécies de enxofre de interesse atmosférico, ácidos metanosulfínico (CH 3 S(O)OH, MSIA) e metanosulfônico (CH 3 S(O) 2 OH, MSA) foram determinadas no nível de CCSD(T)/CBS (coupled-cluster with single and double and perturbative triple excitations/complete basis set) de teoria. Duas conformações foram encontradas para o ácido metanosulfínico e o valor médio determinado para a entalpia de formação foi -337,2 kJ mol -1 . Para o ácido metanosulfônico, o resultado para a entalpia de formação foi 566,2 kJ mol -1 . Escolhendo cuidadosamente as reações químicas e considerando a existência de duas conformações de MSIA, esta investigação reporta os valores mais precisos de DH f disponíveis até agora para estas espécies.The structural, spectroscopic and thermochemical properties of two sulfur species of atmospheric interest, methanesulfinic (CH 3 S(O)OH, MSIA) and methanesulfonic (CH 3 S(O) 2 OH, MSA) acids, were determined at the CCSD(T)/CBS (coupled-cluster with single and double and perturbative triple excitations/complete basis set) level of theory. Two stable conformers were found to the methanesulfinic acid, and the determined average value for the enthalpy of formation (DH f ) was -337.2 kJ mol -1 . For methanesulfonic acid, the determined enthalpy of formation was 566.2 kJ mol -1 . By carefully choosing of the chemical reactions and considering the existence of two MSIA conformers, this investigation reports the most accurate DH f values available to date for these species. Keywords: dimethyl sulfide, enthalpy of formation, CCSD(T)/CBS theory IntroductionDimethyl sulfide (DMS), generated in the ocean by phytoplankton, is an important natural source of sulfur in the atmosphere. 1 The main final products of its atmospheric decomposition are sulfuric acid and sulfate ions, which are key species in the climate regulation, due to the fact that they are precursors of aerosols. Sulfur aerosols act in the global warming producing a negative radiative forcing, dispersing the solar radiation and increasing the albedo. 2 Besides, due to the low gas pressure and polarity, these species can act as cloud condensation nuclei (CCN), condensing water molecules. 3,4 Several experimental and theoretical investigations of the oxidation of DMS in gas phase were conducted 5-7 and studies for OH-initiated reaction had revealed methanesulfonic acid (CH 3 S(O) 2 OH, MSA) 8 and methanesulfinic acid (CH 3 S(O) OH, MSIA) 9 as two key intermediates. In general, there are some difficulties in the characterization of the products, and the values of product yields reported can differ significantly. It is generally accepted that MSA is produced from the OH addition to DMS, in a mechanism highly dependent on temperature and O 2 partial pressure. On the other hand, the presence of MSIA in the atmospheric decomposition of DMS was proposed by Yin et al., 10 as a second-generation product of the DMS oxidation. However, the mechanism and the yields of MSIA formation were reasons of ...