The spectroscopic (FT-IR, FT-Raman and NMR), first order hyperpolarizability and HOMO–LUMO analysis of 2-mercapto-4(3H)-quinazolinone

• The complete vibrational assignments of 2MQ have been made based on PED.
• The experimental and theoretical data comparisons confirm the accuracy of DFT calculations.
• MESP visualization of 2MQ helps to predict its reactive behavior in both electrophilic and nucleophilic reactions.
• HOMO and LUMO energies are predicted and NBO analysis is carried out.

The FTIR and FT-Raman spectra of 2-mercapto-4(3H) quinazolinone have been recorded in the region 4000–450 and 4000–100 cm−1, respectively. The optimized geometry, frequency and intensity of the vibrational bands of 2-mercapto-4(3H) quinazolinone (2MQ) were obtained by the density functional theory (DFT) using 6-311++G(d,p) basis set. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FTIR and FT-Raman spectra. The 1H and 13C nuclear magnetic resonance chemical shifts of the molecule were also calculated using the gauge independent atomic orbital (GIAO) method. The theoretical UV–VIS spectrum of the compound and the electronic properties, such as HOMO (highest occupied molecular orbital) and LUMO (lowest occupied molecular orbital) energies were performed by time-dependent DFT (TD-DFT) approach. The change in electron density (ED) in the σ* antibonding orbitals and stabilization energies E(2) have been calculated by natural bond (NBO) analysis, to give clear evidence of stabilization originating in the hyper conjugation of hydrogen-bonded interactions. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecule has been obtained by mapping electron density isosurface with molecular electrostatic potential (MESP).

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