Tautomeric and conformational equilibrium of acenaphthenequinonemonooxime

The tautomeric and conformational equilibrium of acenaphthenequinonemonooxime was studied by liquid and solid state NMR spectroscopy and ab initio calculations. The compound studied exists in the solid state as a oxime tautomer. However, in solution both the oxime and the nitroso tautomeric forms are present. Ab initio 6-31G(d,p) calculations in agreement with the experimental data predict the oxime tautomer to be more stable. The calculations in CCl4 and DMSO solutions (SCRF model) showed a decrease in the tautomerization barrier with increasing solvent polarity. It is also found that the oxime tautomer exists as two isomers. The calculated energy difference between the isomers is small and decreases upon increasing the solvent polarity. (C) 1999 Elsevier Science B.V. All rights reserved.