Synthesis and characterization of an anticoagulant 4-hydroxy-1-thiocoumarin by FTIR, FT-Raman, NMR, DFT, NBO and HOMO–LUMO analysis

Experimental and theoretical investigations on the molecular structural, electronic and the vibrational characteristics of 4-hydroxy-1-thiocoumarin are presented. Conformational analysis was carried out to obtain the more stable configuration of the compound. The vibrational frequencies were obtained by DFT/B3LYP calculations employing 6-311++G(d,p), 6-31G(d,p), cc-pVTZ basic sets and B3PW91 method with 6-311++G(d,p) basis set and are compared with FTIR and FT-Raman spectral data recorded in the region of 4000–400 and 4000–100 cm−1, respectively. The total electron density and molecular electrostatic potential surfaces of the molecule were constructed to display electrostatic potential (electron + nuclei) distribution. The electronic properties HOMO and LUMO energies were measured. 1H and 13C NMR spectra were recorded and 1H and 13C nuclear magnetic resonance chemical shifts of the molecule were calculated by using the Gauge-Independent Atomic Orbital (GIAO) method and analyzed. The picture of localized bonds and lone pairs, stabilization energy of the delocalization of electrons, the charge and hybridisation of the atoms of 4-hydroxy-1-thiocoumarin were clearly explained by NBO analysis.

► FTIR, FT-Raman and NMR investigations of 4-hydroxy-1-thiocoumarin were carried out.
► A reduction in the bond angle S1–C2–O16 (117.3°) is due to the high electronegativities of sulfur and oxygen atoms.
► 1H and 13C NMR chemical shifts and the electronic transitions of the molecule were discussed.
► The intramolecular charge transfer from π(C3–C4) to π*(C2–O16) has stabilization energy of 22.37 kcal mol−1.
► B3LYP method with 6-311++G(d,p) and cc-pVTZ basis sets are more reliable.