Does tautomeric equilibrium exist in ortho-nitrosonaphthols?

The structure and conformational equilibrium of the monooximes of 1,2-naphthoquinone were studied by solid and liquid state NMR spectroscopy and non-empirical quantum-chemical calculations. According to the experimental data and the ab initio (HF/6-31G** and MP4(SDTQ)/6-31G**//6-31G** levels) calculations the compounds studied exist in the gas phase and in solution as oxime tautomers only. The relative stabilities of the above compounds in chloroform and dimethylsulfoxide solution are calculated within the polarizable continuum model. Solvent effects are found to change the relative stability of the syn- and anti-isomers of 1,2-naphthoquinone-2-oxime. The presence of syn - and antioxime isomers of 1,2-naphthoquinone-2-oxime and two rotameric forms of syn-1,2-naphthoquinone-1-oxime in solution is proved by NMR spectroscopy. (C) 2001 Elsevier Science B.V. All rights reserved.