Estudo termoquímico de tiofenóis substituídos usando DFT e quimiometria

Abstract

Compounds containing the sulfhydryl group (S–H) have aroused interest in the scientific community because they are important reagents in biochemistry, drug production and environmental sciences, due to their oxidizing action, in addition to other chemical properties. When thiophenols receive electron-withdrawing substituents, they have the effect of stabilizing the monomer, increasing the strength of the S–H bond. For electron-donating substituents, thiophenol is destabilized, with a decrease in the strength of the S–H bond. The chemical effects that occur in substituted thiophenol are investigated in this work, with three electron-withdrawing and three electron-donating substituents. The experimental thermochemical study of the dissociation reaction of hydrogen from the sulfhydryl group is not very accessible due to the high level of toxicity of these compounds, as well as the technical difficulty of monitoring this photochemical reaction in calorimetric systems. Therefore, the study of the thermochemical properties of S–H bond cleavage carried out by density functional theory has stood out with publications in specialized journals as an important alternative for investigating this type of system. This work aims to study the thermochemistry of the hydrogen dissociation reaction of the S–H group of eighteen substituted thiophenols, with the substituents: fluorine, bromine, chlorine, methyl, amino and methoxy, in the ortho, meta and para positions. The methodology used was Density Functional Theory with the hybrid functionals B3LYP, ωb97X-D3 and B2PLYP-D3, associated with four sets of Pople basis functions. The inductive effect of electron-withdrawing halogens of the aromatic ring has been well described by DFT methodology. NH2-ArSH was the least stable species among the substituted thiophenols. The electron donating effect of amino and methoxy, from the mesomeric effect, in the ortho and para positions were observed in the theoretical results obtained in this work. The effect of hyperconjugation of the methyl substituent as an electron donor to the aromatic ring was not observed in the calculations obtained.