MOLECULAR STRUCTURE, VIBRATIONAL SPECTRA [FT-IR AND FT-RAMAN], ELECTRONIC SPECTRA [UV-VISIBLE] AND NMR ANALYSIS ON HYDROQUINONE USING HF AND DFT CALCULATIONS

Abstract: The FT-IR spectrum of Hydroquinone was recorded in the region 4000-100 cm-1. The FT-Raman spectrum of Hydroquinone was also recorded in the region 4000-100 cm-1. Quantum chemical calculations of energies, geometrical structure and vibrational wave numbers of Hydroquinone were carried out by HF and DFT methods with 6-311++G(d,p) basis sets and the corresponding results were tabulated. The difference between the observed and scaled wave number values of most of the fundamentals is very small. Moreover, 13C NMR and 1H NMR were calculated by using the gauge independent atomic orbital method with B3LYP methods and the 6-311++G(d,p) basis set and their spectra were simulated and the chemical shifts linked to TMS were compared. A study on the electronic and optical properties; absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies were carried out. The kubo energy gap of the present compound was calculated related to HOMO and LUMO energies which confirm the occurring of charge transformation. Besides Frontier Molecular Orbital's (FMO), Molecular Electrostatic Potential was performed. The NLO properties related to Polarizability and hyperpolarizability based on the finite-field approach were also discussed. A detailed interpretation of the infrared and Raman spectra of Hydroquinone is also reported based on total energy distribution. The calculated HOMO and LUMO energies shows that charge transfer occur within the molecule. The theoretical FT-IR and FT-Raman spectra for the title compound have also been constructed. The thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures were calculated in gas phase.

Keywords: Hydroquinone; HOMO-LUMO; optical properties; GIAO; NLO; Chemical shifts.