Title : Structure and vibrational assignment of the enol form of 1,1,1-trifluoro-2,4-pentanedione ( Structure and vibrational assignment of the enol form of 1,1,1-trifluoro-2,4-pentanedione )
Authors: منصوره زاهدی , Farba Tayyari , Zainab Moosavi-Tekyeh , Alireza Jalali , Sayyed Faramarz Tayyari ,
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Abstract
Molecular structure of 1,1,1-trifluoro-pentane-2,4-dione, known as trifluoro-acetylacetone (TFAA), has been investigated by means of Density Functional Theory (DFT) calculations and the results were compared with those of acetylacetone (AA) and hexafluoro-acetylacetone (HFAA). The harmonic vibrational frequencies of both stable cis-enol forms were calculated at B3LYP level of theory using 6-31G** and 6-311++G** basis sets.We also calculated the anharmonic frequencies at B3LYP/6-31G** level of theory for both stable cis-enol isomers. The calculated frequencies, Raman and IR intensities, and depolarization ratios were compared with the experimental results. The energy difference between the two stable cis-enol forms, calculated at B3LYP/6-311++G**, is only 5.89 kJ/mol. The observed vibrational frequencies and Raman and IR intensities are in excellent agreement with the corresponding values calculated for the most stable conformation, 2TFAA. According to the theoretical calculations, the hydrogen bond strength for the most stable conformer is 57 kJ/mol, about 9.5 kJ/mol less than that of AA and about 14.5 kJ/mol more than that of HFAA. These hydrogen bond strengths are consistent with the frequency shifts for OH/OD stretching and OH/OD out-of-plane bending modes upon substitution of CH3 groups with CF3 groups. By comparing the vibrational spectra of both theoretical and experimental data, it was concluded that 2TFAA is the dominant isomer.
Keywords
, Vibrational spectra; Trifluoro, acetylacetone; Density functional theory; Intramolecular hydrogen bond; anharmonicity 1. Introduction It is well known that the cis, enol form of , diketones is characterized by a strong intramolecular hydrogen bond [1–4]. The simplest members of this class of com
@article{paperid:202490,
author = {منصوره زاهدی and Farba Tayyari and Zainab Moosavi-Tekyeh and Alireza Jalali and Tayyari, Sayyed Faramarz},
title = {Structure and vibrational assignment of the enol form of 1,1,1-trifluoro-2,4-pentanedione},
journal = {Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy},
year = {2006},
volume = {65},
month = {March},
issn = {1386-1425},
pages = {387--396},
numpages = {9},
keywords = {Vibrational spectra; Trifluoro-acetylacetone; Density functional theory; Intramolecular hydrogen bond; anharmonicity
1. Introduction
It is well known that the cis-enol form of -diketones is characterized
by a strong intramolecular hydrogen bond [1–4]. The
simplest members of this class of compounds are malonaldehyde
(MA) and acetylacetone (AA); which have been the subject of
many theoretical and experimental studies [5–15]. IR; Raman;
NMR;X-ray; neutron; and electron diffraction studies onAAand
its derivatives [16–28] indicate that substitution of the methyl
groups of AA has a drastic effect on both the position of ketoenol
equilibrium and the strength of the intramolecular hydrogen
bond. It is well known that the electron-withdrawing substitutes;
such as fluorine atom; increase the enol content of -diketones
[26–30]. By means of vibrational spectroscopy [4;17;19;20];
∗ Corresponding},
}
%0 Journal Article
%T Structure and vibrational assignment of the enol form of 1,1,1-trifluoro-2,4-pentanedione
%A منصوره زاهدی
%A Farba Tayyari
%A Zainab Moosavi-Tekyeh
%A Alireza Jalali
%A Tayyari, Sayyed Faramarz
%J Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
%@ 1386-1425
%D 2006
