Theoretical and experimental tautomerism study of para-Trifluorobenzoylacetone halogen derivatives using DFT and vibrational spectroscopy

Subject Areas :

Vahidreza Darugar ¹ , Mohammad Vakili ² , Sayyed Faramarz Tayyari ³

1 - Department of chemistry, Faculty of science, Ferdowsi University of Mashhad
2 - Department of chemistry, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran
3 - Department of chemistry, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran

Received: 2019-06-22 Accepted : 2019-08-04 Published : 2019-05-22

Keywords: Density functional theory (DFT), Intramolecular hydrogen bond, Vibrational Assignment, substitution effect,

Abstract :

Analysis of the molecular structure and relative stability for the cis-enol stable forms in trifluorobenzoylacetone and halogenated derivatives was performed by density functional theory (DFT), at level B3LYP / 6-311 ++ G **. In these molecules, there are only two forms of cis-enol that are capable of forming an intra-molecular O-H + O hydrogen bond, which are equilibrium. Our calculations show that the difference between these two forms in para-halotrifluorobenzoylacetone molecules is about 1.49-4.75 kcal/mole, indicating that both forms can exist in the sample. The hydrogen bond strength has also been calculated for the stable enilic forms of this molecule through the AIM software and compared with other parameters related to the hydrogen bond strength, including structural parameters and spectroscopy. According to the results obtained in para-halogenated trifluorobenzoylacetone molecules, the hydrogen bond strength in form-2 is greater than Form-4. Comparison of these results also shows that the chlorine, fluorine and bromine substituents in the para position of phenyl ring have no significant effect on the structure and intramolecular hydrogen bond strength, but can lead to the displacement the bands of the phenyl ring.