Original scientific paper

Substituent, Temperature and Solvent Effects on Keto-Enol Equilibrium in Symmetrical Pentane-1,3,5-triones. Nuclear Magnetic Resonance and Theoretical Studies

Predrag Novak ; Ruđer Bošković Institute, P. O. Box 180, HR-10002 Zagreb, Croatia
Danko Škare ; Ruđer Bošković Institute, P. O. Box 180, HR-10002 Zagreb, Croatia
Sanja Sekušak ; Ruđer Bošković Institute, P. O. Box 180, HR-10002 Zagreb, Croatia
Dražen Vikić-Topić ; Ruđer Bošković Institute, P. O. Box 180, HR-10002 Zagreb, Croatia

Abstract

Keto-enol tautomeric equilibrium in several β-triketones has been investigated using NMR spectroscopy and theoretical methods. The equilibrium involves two slow and two fast enolization processes in solution. In solvents of low polarity and at room temperature, the predominant tautomeric species is the dienol form. However, the equilibrium is significantly shifted to the more polar triketo form on raising the temperature up to 140 °C and by using solvents of higher polarity. Structures and stabilities of both long-and short-lived tautomeric forms, as well as transition-state structures and barrier heights of enolization processes, were calculated using semiempirical and density functional quantum Chemical methods.

Keywords

pentane-1,3,5-triones; keto-enol equilibrium; nuclear magnetic resonance spectroscopy; quantum Chemical calculations

Hrčak ID:

131995

URI

https://hrcak.srce.hr/131995

Publication date:

4.12.2000.

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