A study of pyrazolin-5-one tautomerism. Part IV. Natural abundance carbon-13 nuclear magnetic resonance spectra

Abstract

Natural abundance ¹³C n.m.r. spectra have been recorded for four 1-phenyl-2-pyrazolin-5-ones and one 1-phenyl-3-pyrazolin-5-one in dimethyl sulphoxide solution. Examination of the spectra, with particular emphasis on the carbonyl region, permits the tautomeric forms of the compounds to be assigned without reference to other techniques. The parent compound and the 3-substituted methyl and ethoxycarbonyl derivatives exist in the OH form, whilst the 3-amino-compound exists in the CH form under the experimental conditions employed.