A structural and spectroscopic study on para-aminohippuric acid with experimental and theoretical approaches

In this work, the molecular conformation, vibrational and electronic analysis of para-aminohippuric acid (pAHA, C9H10N2O3) were presented for the ground state using experimental techniques (FT-IR, FT-Raman and UV) and density functional theory (DFT) employing B3LYP exchange correlation with the 6-311++G(d,p) basis set. FT-IR and FT-Raman spectra were recorded in the regions of 400–4000 cm−1 and 50–4000 cm−1, respectively. The UV absorption spectra of the compound that dissolved in ethanol and water solution were recorded in the range of 190–400 nm. Potential energy curve was computed by means of scanning NCCO torsion angle. The geometry optimization and the energies associated possible four conformers (C1–C4) were computed. The computational results diagnose the most stable conformer of pAHA as the C1 form. Optimized structure of compound was interpreted and compared with the earlier reported experimental values. The complete assignments of fundamental vibrations were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. A study on the electronic properties, such as frontier molecular energies, absorption wavelengths and oscillator strengths, were predicted by time-dependent DFT (TD-DFT) approach, while taking solvent effects into account. To investigate non-linear optical properties: polarizability, anisotropy of polarizability and molecular first hyperpolarizability of molecule were computed. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures were calculated.

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► The spectroscopic properties of para-amino hippuric acid were examined by FT-IR, FT-Raman and UV techniques and DFT/B3LYP method.
► The complete assignments are performed on the basis of the total energy distribution (TED).
► HOMO and LUMO energies, absorption wavelength and excitation energies were calculated.
► Polarizability and first hyperpolarizability of para-amino hippuric acid were calculated.
► Thermodynamic properties and their correlations with temperature were obtained from the theoretical vibrations.