Abordagem teórica do equilíbrio E/Z de tiossemicarbazonas derivadas do 2-acetiltiofeno

Abstract

Due to their pharmacological and medicinal properties, thiosemicarbazones (TSCs) have been the subject of many studies. Their structures allow configurational isomerism resulting in the entgegen (E) and zusammen (Z) forms. In this work, the 2- acetylthiophene thiosemicarbazone (ATTSC) and their N-Terminal substituents ATTSC-CH 3 and ATTSC-Ph were investigated in the gas phase and in condensed phase through the SMD continuum solvation model for water, DMSO and cyclohexane. The conformational analysis was performed in a first stage through the use of the PM3 semi-empirical method. Afterward, subsequent optimizations and harmonic frequencies evaluation were carried out through the Density Functional Theory (DFT), at B3LYP/ 6-31+G(d,p) level of theory. Among several possible structures, the present work was focused in the Z or E descriptors related to the N 2 -N 3 -C 2 -R 2 dihedral for which six stationary points were identified. For this particular dihedral and descriptors, a majority population for the E form was identified and an interconversion pathway was proposed. Natural bonding orbitals (NBO) analysis were used in order to explain the stability of certain structures in what concerns the stabilizing (hyperconjugations) and destabilizing effects (repulsive forces). The conducted study can aid future investigations related to the coordination mode in chemical systems for which the TSC studied can be employed as a ligand. Beyond the E and Z geometries related to the N 2 -N 3 -C 2 -R 2 dihedral, other spatial arrangements related to other E and Z descriptors were also identified along the study.