Estudo teórico da energia de dissociação da ligação S–H de tiofenóis substituídos em fase gasosa

Abstract

Benzene's structure is susceptible to electrophilic attack, essentially, because of its exposed π electrons. Therefore, substituents are commonly found in its structure, in the ortho, meta and para positions. This work aimed to investigate through the Density Functional Theory with the B3LYP functional the dissociation reaction of the H atom in the S–H bond of bromothiophenol, methylthiophenol, methoxythiophenol and aminothiophenol, in gas phase, with the substituents in the ortho positions , goal and stop. The S–H bond dissociation reaction leads to the formation of the thiol radical, which is recognized by its antioxidant activity and the magnitude of this activity can be estimated by the variation of the homolytic dissociation enthalpy of the S–H bond. The aforementioned reaction is spin prohibited and the study of the potential energy curves of the reaction path were calculated by the ground state Density Functional Theory in order to study the dissociation reaction of the S–H bond and describe the intersystem crossing between singlet and triplet spin states related to the effect of the substituent. The Density Functional Theory with the calculation level used in this work presented satisfactory results when compared with the experimental values found in the literature. It was found that any of the substituents in the para position has the greatest effect of the substituent when compared to the other positions, in which there is a decrease in dissociation energy, which favors the breaking of the S–H bond. While in meta position the stability of thiophenols is observed.