Molecular analyses using FT-IR, FT-Raman and UV spectral investigation; quantum chemical calculations of dimethyl phthalate

Abstract

Dimethyl phthalate C6H4 (COOCH3)2 (DIMPHT) has been synthesized. To characterize molecular functional groups FT-IR and FT-Raman spectrum were recorded and wavenumbers were assigned accordingly. The optimized geometrical parameters, vibrational assignments, chemical shifts and thermodynamic properties of title compound were computed by ab-initio calculations at Density Functional Theory (DFT/B3LYP) method with 6–311++G(d,p) as basis set. The potential energy curve expresses that DIMPHT molecule has three stable structures. The computational results diagnose the most stable conformer of the DIMPHT as the conformer 2 of the compound. The calculated harmonic wavenumbers of compound were then analyzed in comparison to experimental FT-IR and Raman spectrum. Gauge independent atomic orbital (GIAO) method was used for determining, (1H) and carbon (13C) nuclear magnetic resonance (NMR) spectra of the molecule. Molecular parameters were calculated along with its periodic boundary conditions calculation (PBC) analysis supported by X-ray diffraction studies. The frontier molecular orbital (HOMO, LUMO) analysis describes charge distribution and stability of the molecule which concluded that nucleophilic substitution is more preferred and the mullikan charge analysis also confirmed the same. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) complements with the experimental findings. In addition, molecular electrostatic potential, nonlinear optical and thermodynamic properties of the title compound were performed. Mulliken and natural charges of the title molecule were also calculated and interpreted. The effects of the computations were applied to theoretical spectra of the title compound, which show excellent agreement with observed spectra. The scaled B3LYP/6-311++G(d,p) results show the best arrangement with the experimental values over the other method.