Geometric isomerism in the series of fluoroalkyl-containing 1,2,3-trione 2-arylhydrazones

According to the H-1, C-13, and F-19 NMR data, fluoroalkyl-containing 1,2,3-trione 2-arylhydrazones in CDCl3 exist exclusively, while in (CD3)(2)CO Preferentially, as isomers in which the acyl or aroyl group is involved in intramolecular hydrogen bond. The isomer structure was assigned on the basis of the chemical shifts of the carbonyl carbon atoms and fluorine atoms and carbon-fluorine spin-spin coupling constants J(C-F). X-ray diffraction data showed that 1,2,3-trione 2-arylhydrazones in crystal have the same structure as in CDCl3 solution. Quantum-chemical calculations were performed to rationalize predominant formation of 1,2,3-trione 2-arylhydrazone isomers with a free polyfluoroacyl group.