Vibrational (FT-IR and FT-Raman), electronic (UV-vis) and quantum chemical investigations on pyrogallol: A study on benzenetriol dimers

Pyrogallol was identified for the first time from the natural extract of Abrus precatorius Linn seeds using GC-MS technique. The vibrational analysis of pyrogallol was investigated in solid phase by FT-IR and FT-Raman spectroscopic techniques in the region 4000-400 cm(-1) and 4000-40 cm(-1), respectively. The optimized molecular geometry, wave number and intensity of the vibrational bands of pyrogallol and its isomers were obtained by DFT method with different basis sets. The electronic transition energy and intensities, HOMO-LUMO energy gap have been computed with the ZINDO, CIS, TDDFT theory for isomers and the differences were compared with UV-vis absorption spectra. The observed wave numbers in FT-IR, FT-Raman and UV-vis spectra were analyzed and assigned to various fundamental modes of vibration in the molecules. Experimentally observed vibrational frequencies and electronic transitions were assigned with the help of theoretical vibrational and electronic spectra, respectively. The differences between observed and calculated wave number values of most of the fundamental modes are very small. The calculated parameters were found to be in best agreement with experimental findings, thereby confirming the monomer and dimer structure of the identified molecule as well as its isomers. (C) 2018 Elsevier B.V. All rights reserved.