Tautomerization and Intramolecular Hydrogen bond Strength of para Chlorine-Benzoylacetone by Quantum Computation and Spectrometry Results

Subject Areas :

Vahidreza Darugar ¹ , Mohammad Vakili ² , Hosein Eshghi ³

1 - Department of chemistry, Faculty of science, Ferdowsi University of Mashhad
2 - Department of chemistry, Faculty of sciences, Ferdowsi University of Mashhad.
3 - Department of chemistry, Faculty of sciences, Ferdowsi university of Mashhad.

Received: 2017-06-24 Accepted : 2017-12-30 Published : 2017-08-23

Keywords: substitution effect, Intramolecular hydrogen bond, Spectroscopy, DFT,

Abstract :

Molecular structure analysis and relative stabilities for stable cis-enol forms of benzoylacetone(BA) and para chloro-benzoylacetone (Cl-BA) molecules were performed by density functional theory (DFT) at B3LYP/6-311++G** level of theory. In these molecules, there are only two stable cis-enol (chelated) forms with the intramolecular hydrogen bond (O-H...O) and an equilibrium between them. Our calculations show that the energy difference between these two forms in the para-chloro-benzoylacetone molecule is about 0.8 kcal/mol. Therefore, coexisting of two stable cis-enol forms of para-chloro-benzoylacetone in the sample is possible. The hydrogen bonding strength has also been calculated for the stable enolic formations of this molecule. The intramolecular hydrogen bond strength of the mentioned forms obtained by AIM software. We compared the AIM results with the other parameters related to the hydrogen bond strength, including geometrical and spectroscopic parameters. According to the our results, in benzoylacetone and chloro-benzoylacetone molecules, the intramolecular hydrogen bond strength in 4 form is greater than that in 2 form. The comparison of these results also shows that the chlorine substituent in the para position of phenyl ring does not have any significant effect on the structure and intramolecular hydrogen bond strength.