Infrared and photoelectron spectra, and keto—enol tautomerism of acetylacetones and acetoacetic esters

Abstract

The infrared and photoelectron spectra of some substituted acetylacetones have been measured, and interpreted in terms of enolic and ketonic structures. Ionization potentials from specific orbitals have been assigned. With different substituents, the proportion of the two forms varies considerably. From measurements of the photoelectron spectrum over a wide temperature range, the equilibrium constants for keto-enol forms have been determined and estimates made of the enthalpy of the tautomeric change. Conclusions about the tautomerism have been correlated with earlier measurements by other methods. For comparison, the spectra of acetoacetic esters and related compounds have been measured. The proportions of keto-enol forms have been estimated and ionization potentials assigned to particular orbitals.