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 41.08kJmol - 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 (2.06Å) intramolecular hydrogen bond. The X-ray determined crystal structure shows extended three-dimensional network comprising of C O...H intermolecular hydrogen bonds (1.87Å) 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 3125cm - 1 in the measured infrared spectrum whereas the 3365cm - 1 peak originates from the associated OH stretching.