A combined experimental and theoretical approach is presented to structural characterization of fairly large, newly synthesized organic molecules in order to enhance the effectiveness of their instrumental analysis by vibrational spectroscopy. The method consists of measurement of FT-IR and Raman spectra of the reaction products and subsequent ab initio or DFT quantum mechanical calculations (prediction) of the vibrational spectra for any anticipated structural varieties of the synthesized molecules. Comparison of the measured and computed frequencies as well as the observed and simulated spectra is performed to resolve any uncertainties in identifying the reaction products. Vibrational frequency and normal mode calculations based on scaled quantum mechanical (SQM) force fields performed at the DFT/B3LYP/6-31G* level of theory are demonstrated to provide a wealth of information that have been used in this work to ascertain the molecular structure, probable conformation and H-bond properties of three new isochromanone or coumarin derivatives, namely: 3-([2′-hydroxymethyl]-phenyl)-coumarin (1), E-4-(3′-hydroxyphenylmethylene)-3-isochromanone (2), and 2-[(2′-hydroxymethyl)phenyl]-3H-naphto[2,1-b]pyran-3-one (3).
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