Does tautomeric equilibrium exist in 4-nitroso-5-pyrazolones?

The calculated relative energies of the tautomers and isomers of 3-methyl-4-nitroso-5-pyrazolone and 1-ethyl-3-methyl-4-nitroso-5-pyrazolone suggest that in solution the oxime tautomer is favoured. The second compound exists as a mixture of syn- and anti-oxime isomers. The coexistence of the oxime forms in solution corresponds to the available experimental NMR data.