Chemical Stability of Imidazole-Thiosemicarbazides in Solvents: NBO Studies and Theoretical Absorption Spectrum

Abstract

This study of chemical stability in solvents was performed on four (4) molecules of a series of halogen-substituted imidazole-thiosemicarbazides (IT) using the TD-DFT method at the B3LYP/6-31+G (d, p) level. The solubility of the imidazole-thiosemicarbazides in solvents across the dipole moment revealed that the ITs have the lowest values of the dipole moment in cyclohexane, indicating that the ITs are more soluble in cyclohexane. This claim was confirmed by the assessment of the energy gap in the different solvents. Analysis of the effect of temperature on the stability of imidazole-thiosemicarbazides showed that temperature has no effect on the stability of the ITs studied. This observation could allow to fight effectively against the different bacteria and to control their storage conditions and also to establish their expiry dates. The NBO analysis and the study of the absorption spectrum were also carried out in order to show the hyperconjugative interactions and the delocalization of atomic charges. In this case, the stabilizing interactions involve the free pairs of nitrogen atoms N16 and N19 and the antibinding single bond are σ*(C18-S21). Analysis of the theoretical absorption spectrum showed that the absorption band representing cyclohexane is more intense for all the compounds studied. This is because cyclohexane better promotes the stabilization of substituted imidazole-thiosemicarbazides. Moreover, the maximum band corresponds to the electronic transition between the HOMO and the LUMO is due to an electron displacement from the LP (N) orbitals towards the σ*(CS) orbitals.