Abstract

The prototropic tautomerism of 3-methyl-5-pyrazolone was studied by using Density Functional Theory along with (1)H, (13)C and (15)N-NMR. The results show that for the isolated molecule and low polarity solvent the 5PYR-1 tautomer, a keto form, is the predominant species. In DMSO solution the predominant tautomeric form is 5PYR3, a hydroxy tautomeric species. For almost every atom an excellent agreement was found between the experimental and calculated NMR spectra using GIAO method at DFT/ B3LYP/6-311+G (2p,d) level.