The Assignment of UV Spectra and the Tautomeric Equilibria of Unsymmetrical β-Diketones -2-Furoyltrifluoroacetone, Benzoyltrifluoroacetone, and 2-Thenoyltrifluoroacetone-

Abstract

Electronic spectra of 2-furoyltrifluoroacetone (FTA), benzoyltrifluoroacetone (BFA), and 2-thenoyltrifluoroacetone (TTA) were measured in several solvents. Of the three β-diketones studied, FTA was the most sensitive to the solvent effect examined. The spectra of FTA in heptane showed two maxima at 320nm and 345nm, both bands being resolved into two sub-sidary bands (see Fig. 1). The spectra in acetonitrile, on the other hand, two broad bands at 320 nm and 350 nm with no subsidary bands (see Fig. 1). Moreover, the comparison of the relative intensities of two maxima in acetonitrile with those in heptane showed that they were inverted (see Fig. 4). These facts suggest the presence of the equilibrium between two or more tautomers. For the interpretation of the spectra at the low concentrations in inert solvents, equilibria between two cyclic enol structures ([A] and [B]) were postulated for these β-diketones, and spectra of those were reasonably assigned by means of an ASMO SCF-CI calculation (Table 1).