Theoretical and experimental investigations on the structure and vibrational spectra of 2-hydroxy-3-methyl-1,4-naphthoquinone-1-oxime

Abstract

Hartree–Fock and hybrid density functional methods have been used to determine the structure and energetics of keto and nitrosophenol tautomers of 2-hydroxy-3-methyl-1,4-naphthoquinone-1-oxime ( 1). The charge distribution and vibrational spectra of keto form of 1 have been studied. The structure derived from X-ray diffraction on the single crystal has also been presented. Both the theory and experiment predict that 1 exists predominantly as amphi conformer (keto form), which is 23.54 and 41.08 kJ mol −1 more stable relative to the anti and syn conformers, respectively. This has partly been attributed to the five-membered ring formation resulting from the N⋯H–O (2.06 Å) intramolecular hydrogen bond. The X-ray determined crystal structure shows extended three-dimensional network comprising of CO⋯H intermolecular hydrogen bonds (1.87 Å) as well. Quantum mechanically calculated molecular electrostatic potential investigations provide insights for the formation of supramolecular assemblies. The frequencies of the CN and CO stretching vibrations from the density functional theory agree well with those observed experimentally. The intramolecular hydrogen bonded interactions (N⋯H–O) give a broad band near 3125 cm −1 in the measured infrared spectrum whereas the 3365 cm −1 peak originates from the associated OH stretching.