Intramolecular hydrogen-bonding in 2-nitroresorcinol. A combined FT-IR, FT-Raman and computational study Original Research Article

The vibrational properties of 2-nitroresorcinol have been studied by a combined experimental and theoretical analysis. The FT-IR and FT-Raman spectra of the compound have been recorded in the mid- and far-IR range (4000–150 cm−1). Symmetry related experimental information was obtained from polarisation IR and Raman measurements. The interpretation of the spectra was aided by quantum chemical calculations carried out at the B3-LYP/6-31G* level. Both the spectra and calculations support the C2v structure of the molecule with a symmetric intramolecular –O–H⋯O–N–O⋯H–O– hydrogen bonding interaction. The deficiencies of the computations for the molecular vibrations were corrected by the scaled quantum mechanical (SQM) method of Pulay. Using the standard scale factors developed for B3-LYP/6-31G* force fields, an rms deviation of 9.7 cm−1 was achieved between the gas-phase experimental and SQM frequencies. As a result of our SQM analysis, all the 42 fundamentals of the molecule were assigned. A comparison with the analogous hydrogen bonding moiety in 2-nitrophenol indicates a somewhat stronger hydrogen bonding interaction in the title molecule. This is accompanied, however, by an increased strain in the six-membered –C–O–H⋯O–N–C– rings.