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 CO⋯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 CN and CO 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.
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