A spectroscopic approach to compare the quantum chemical calculations and experimental characteristics of some organic molecules; Benzene, Toluene, P-Xylene, P-Toluidine

In this study, first, Benzene molecule pretends as the starting point, and then methyl and amine groups were added to construct Benzene like molecules. After that, the change of the mentioned physical properties above was investigated. In addition, HOMO-LUMO, MEP, and character tables of these organic molecules were obtained, and the effect of group symmetry was investigated. Density functional theory calculations were used in this study to obtain vibrational and electronic spectra for the four ring molecules (Benzene, Toluene, p-Xylene, p-Toluidine) and optimized geometries of molecules were performed in these programs. It was concluded that the molecules belong to D6h, C2v, D2h and C2v symmetry point groups for Benzene, Toluene, p-Xylene, and p-Toluidine respectively. It is concluded that lowest C1-C2 bond was in Benzene and p-Xylene, and the highest C1-C2 bond was in Toluene. On the other hand, it was found out that many vibrational frequencies changed with the addition of subgroups. It was aimed to determine the interaction sites of each molecule. For this purpose, mulliken atomic charges, molecular electrostatic potential (MEP) surface map and quantum chemical properties such as hardness, softness, electronegativity, chemical potential, ionization potential, electrophilic index, dipole moment, electron affinity were calculated via Gaussian program.

Automated summary

In this study, Benzene molecule was used as the starting point to construct Benzene-like molecules by adding methyl and amine groups, and the changes in physical properties were investigated. The study obtained HOMO-LUMO, MEP, and character tables for these organic molecules, and analyzed the effect of group symmetry. Density functional theory calculations were used to obtain vibrational and electronic spectra, and optimized geometries for four ring molecules. The study concluded the symmetries of Benzene, Toluene, p-Xylene, and p-Toluidine as D6h, C2v, D2h, and C2v respectively. It was found that the lowest C1-C2 bond was in Benzene and p-Xylene, while the highest C1-C2 bond was in Toluene. The study also identified changes in vibrational frequencies with the addition of subgroups, and determined the interaction sites of each molecule through various quantum chemical properties.