Ab initio and DFT computational studies on molecular conformations and intramolecular hydrogen bonding in 3-mercapto-but-2-enethial

Abstract

The molecular structure and intramolecular hydrogen bond energies of 20 conformers of 3-mercapto-but-2- enethial were investigated at MP2/6-311 + +G**, B3LYP/6-311 + +G**, and G2MP2 levels of theory. Furthermore, calculations for all the possible conformations of the title compound in water and CCl4 solutions were also carried out at the B3LYP/6-311 + +G** level of theory. The calculated geometrical parameters and conformational analysis in gas phase, water, and in CCl4 solutions showed that the 4- mercapto-but-3-ene-2-thione conformers of this compound are more stable than the others. This stability is mainly due to the formation of an S–H...S intramolecular hydrogen bond, which is assisted by π-electrons resonance. Hydrogen bond energies for all conformers of 3-mercapto-but-2-enethial were obtained from the related rotamers method (RRM). The “atoms in molecules” theory of Bader which is based on topological properties of the electron density (ρ) was used to analyze critical points and to study the nature of hydrogen bond in these systems. Natural bond orbital (NBO) analysis was also performed for better understanding the nature of intramolecular interactions in 3-mercapto-but-2-enethial. The results of these calculations were in agreement with data obtained by the RRM