Theoretical and experimental studies of 5-iodo-salicylic acid molecule using spectroscopic method

In this study, The 5-iodo-salicylic acid (5-ISA, C7H5IO3) was characterized by FT-IR, FT-Raman, NMR and UV spectroscopy. There are eight conformers, Cn, n=1-8 for 5-ISA so that the molecular geometry for these eight conformers in the ground state were calculated by using the ab-initio density functional methods (B3LYP) approach with the aug-cc-pVDZ-PP basis set for iodine and the aug-cc-pVDZ basis set for the other elements. The computational results identified the most stable conformer of 5-ISA as the C1 form. The vibrational spectra calculated DFT method invoking the same basis sets and fundamental vibrations were assigned on the basis of the total energy distribution (TED) of the vibrational modes. Total (TDOS) and partial (PDOS) density of state and also overlap population density of state (COOP or OPDOS) diagrams analysis for C1 conformer were calculated using the same method and also aug-cc-pVDZ-PP pseudo potential for iodine atom and aug-cc-pVDZ for the others. The energy and oscillator strength calculated by time-dependent density functional theory (TD-DFT) results complements with the experimental findings. The NMR chemical shifts (1H and 13C) spectra were recorded and calculated using the gauge independent atomic orbital (GIAO) method. The optimized bond lengths, bond angles and calculated NMR and UV, wavenumbers showed the best agreement with the experimental results. Keywords: 5-iodo-salicylic acid, DFT; NMR, UV, Infrared spectra; HOMO–LUMO, DOS.