Investigação de protocolos de cálculo por métodos de solvatação implícita na previsão do efeito Gauche em 1,2-Di-haloetanos

Abstract

Aiming to improve the compromise between accuracy and low computational cost in conformational analysis of organic compounds, we investigate the performance of a set of calculation protocols based on continuum solvation methods in predicting the Gauche e ect in 1,2-dihaloethanes. To do so, we have set up such protocols by combining solvation methods, radii models, DFT (Density Functional Theory) functionals and basis sets and calculated the energy di erence between the Gauche and Trans conformers in chloroform, dimethylsulfoxide and methanol. In our analysis, we concluded that the UFF (Universal Force Field) and UA0 (United Atom) radii models are not suitable for calculations with DFT functionals, but rather work well with lower level methods, like Hartree-Fock. The 6-31+G* and 6-311+G* basis sets furnished the best average results, in association with the SMD (Density-based Solvation Model) method and M05-2X functional. For 1,2-diiodoethane, the best results are obtained with LanL2DZ pseudopotential. A trend in the improvement of the results for lighter halogens upon the increase of the basis sets and the opposite for the heavier ones was found. We have shown that di use functions play a key role in this kind of analysis, increasing the protocols accuracy. Furthermore, SMD handles the non-electrostatic corrections in a more balanced way between the Gauche and Trans conformers. The results are in good agreement with experimental data, with average errors near to 0,05 kcal mol1, which, in principle, allows us to transfer our conclusions to larger systems, which in turn is one of our future developments.