Conformation, structure, intramolecular hydrogen bonding, and vibrational assignment of 4,4,4-trifluoro-1-(2-furyl)-1,3-butanedione

All the theoretical enol and keto conformations of 4,4,4-trifluoro-1-(2-furyl)-1,3-butanedione, known as furoyltrifluoroacetone (FTFA), have been investigated at the ab initio level using the 6-31G∗∗ basis set. The correlation energy has been evaluated by means of the Becke functional following the density functional theory. It was found that the most stable conformers are those stabilized by the hydrogen bridges. The geometries of the cis-enol conformers engaged in intramolecular hydrogen bond were also fully optimized at the B3LYP level using 6-311G∗∗ and 6-311++G∗∗ basis sets. All calculations suggest that the A1 and B1 conformers (with an energy difference of about 1.4–3.0 kJ/mol) are the most stable forms, which supports by the vibrational spectroscopic results. In addition, the proton transfer, the rotation of furyl ring, and the intramolecular hydrogen bond energy of the molecule were investigated. The vibrational spectroscopic results indicate that the hydrogen bond in FTFA is stronger than that in trifluoroacetylacetone, TFAA, but considerably weaker than that in trifluorobenzoylacetone, TFBA, and acetylacetone, AA. This result is in agreement with the proton chemical shifts data.