NMR and FT-IR Investigation Study and Topological Analysis of Various Conformations of 2,5-dimethyl-2,5-dihydroxyl-1,4-dithian using Density Functional Theory Method

Abstract

Abstract: 1,4-dithian-2,5-dihydroxyl is the major source for the synthesis of sulfur-containing heterocyclic compounds such as thiophene and 1,3-thiazole derivatives, which these compounds are widely used in pharmaceuticals and agricultural industries. Sulfur-containing heterocycles, such as 2-aminothiophene, thiazolidine, oxothiazolidine, and thiazoles, can be comprehensively synthesized from dimerization of the derivatives of 1,4-dithian-2,5- dihydroxyl. FT-IR and NMR spectra of axial and equatorial conformations of 2,5-dimethyl-2,5-dihydroxyl-1,4- dithian compound were investigated by density functional theory (DFT) using B3LYP/6-311++G** and M06- 2X/aug-cc-pVDZ computational methods. The topological properties of the electron charge density were calculated by the quantum theory of atoms in molecules (QTAIM) and non-covalent interactions/reduced electron density gradient (NCI-RDG) theoretical methods. The obtained results of the analyses were also discussed in more detail. The results showed that the steric interactions are more prominent than the van der Waals interactions, and in both conformations, steric interactions are included in the middle of the 1,4-dithian ring and there is hydrogen bonding between hydroxyl groups and 1,4-dithian ring structure heteroatoms in the axial conformation while this interaction is not observed in the case of equatorial conformation. The presence of these interactions was confirmed using NBO analysis.