Ab initio quantum chemical and NMR study of the symmetric monooximes of 1,2,3-phenalenetrione and 1,2,3-indantrione

The possibility for nitroso-oxime tautomerism in symmetric monooximes of 1,2,3-phenalenetrione and 1,2,3-indantrione is studied by means of ab initio quantum chemical methods and NMR spectroscopy. For both compounds, ab initio calculations with different basis sets predict the oxime tautomer as most stable in agreement with the H-1- and C-13-NMR results in CDCl3 and DMSO-d(6) solutions. A coalescence of the signals for the carbon atoms from carbonyl groups of 1,2,3 phenalenetrione mono-oxime in DMSO-d(6) solution at temperature 360 K is observed. This coalescence may be attributed to rotation of the hydrogen atom from the hydroxyl group around the N-O bond. The rotational transition structures for both compounds at different computational levels were located in the gas phase and in solution. (C) 1998 Elsevier Science B.V.