Study of the tautomerics equilibria of 4-methyl-3-oxo-4-pentenonitrile: solvent and temperature effect

JUAN M GIUSSI; CORTIZO M SUSANA; PATRICIA E. ALLEGRETTI

Florianópolis

Conferencia; 10th Latin American Conference on Physical Organic Chemistry; 2009

b-ketoesters and b-ketonotriles have tautomeric forms in equilibrium and the proportion of these forms depends, among other factors, the polarity of the solvent in which they are situated and the temperature1. Have determined the equilibrium constants for the tautomers in unsaturated b - ketoesteres, such as ethyl 3-oxo-4-pentenoate by nuclear magnetic resonance (NMR) spectrometry, and then study these compounds as monomers in radical polymerization2,3, giving polymers with interesting technological applications4. This study has not been done so far to unsaturated b-ketonitriles. We have synthesized 4-methyl-3-oxo-4-pentenonitrilo, through the adaptation of a method found in the literature for a similar compound 5. This compound presents six possible theoretical tautomers, keto-nitrile, nitrile-enol (E and Z), keto-ketenimine, keto-ynamine and enol-ketenimine. The study of the equilibrium was performed in gas phase by gas cromatography-mass spectrometry (GC-MS), and in solution by proton nuclear magnetic resonance spectrometry (1H-NMR). The experimental results in gas phase were compared with AM1 semiempiric calculation. Interpreting the mass spectrum, tautomer keto-nitrile, nitrile-enol (E and Z) and keto-ketenimine were present. Peaks corresponding only to the tautomers enol-ketenimine and keto-ynamine could not be asigned. In gas phase at the tautomer keto-nitrile is favored. These results are supported by theoretical calculations. The values for the experimental heats of tautomerization are in excellent agreement with the theoretical ones. 1H-NMR spectrum of this compound, in which there were signals of enol-nitrile and keto-nitrile tautomers as overlapping spectra. The operational equilibrium constant (KT) has been studied as the ratio of areas obtained by integration of peaks at d = 4.37, corresponding to hydrogen of =CH- from enol-nitrile tautomer and d = 3.81, corresponding to the hydrogen-CH2- from keto-nitrile tautomer. Heats of tautomerization ketonitrile-enolnitrile have been calculated and comparative with heats of tautomerization in gas phase for evaluate the solvent effect.