Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2018
An interpretation of the experimental IR and Raman spectra of Aluminum (III) trifluoroacetylaceto... more An interpretation of the experimental IR and Raman spectra of Aluminum (III) trifluoroacetylacetonate (Al(TFAA)3) complex, which were synthesized by us, is first reported here. The charge distribution, isomerism, strength of metal‑oxygen binding and vibrational spectral properties for this complex structure were theoretically investigated through population analysis, geometry optimization and harmonic frequency calculations, performed at B3LYP/6-311G* level of theory. In the population analysis, two different approaches reffered to as "Atoms in molecules (AIM)", and "Natural Bond Orbital (NBO)" were used. According to the calculation resuls, the energy difference between the cis and trans isomers of Al(TFAA)3 is very small and indicates that both isomers coexist in the sample in comparable proportions. Comparison of the calculated frequency and intensity data with the observed IR and Raman spectra of the complex has supported this conclusion. On the other hand, comparison of the structural and vibrational spectral data of Al(TFAA)3, which were experimentally measured and calculated at B3LYP/6-311G* level, with the corresponding data of Aluminum acetylacetonate (Al(AA)3) has revealed the effects of CF3 substitution on the structural and vibrational spectral data associated with the CH3 groups in the complex structure.
Molecular structure and vibrational spectra of acetone, acetone-d3, and acetone-d6 were investiga... more Molecular structure and vibrational spectra of acetone, acetone-d3, and acetone-d6 were investigated by means of ab initio and density functional theory (DFT) calculations. The harmonic and anharmonic vibrational frequencies of the acetone isotopomers were calculated at the B3LYP (using the 6–311++G(3df,3pd) basis set) and B2PLYP (using the 6–31+(2d,p) and 6–311G(2df,p) basis sets) levels. The calculated frequencies and the Raman and infrared (IR) intensities were compared with the experimental results. Excellent agreement between calculated and observed vibrational wavenumbers was obtained. Additionally, a normal coordinate analysis (NCA) was also done by using the normal mode eigenvectors obtained at the B3LYP/6–311++G(3df,3pd) level. All fundamental vibrational bands were assigned to the normal modes with the aid of the potential energy distribution (PED) values obtained from normal coordinate calculations. To study the internal rotation of CH3 groups, single CH3 rotation and syn...
FTIR and Raman spectra of an anti-bacterial compound, N-phenylthiobenzamide (NptbH), were recorde... more FTIR and Raman spectra of an anti-bacterial compound, N-phenylthiobenzamide (NptbH), were recorded in the solid phase and in solution. The harmonic vibration wavenumbers, for both the tautomeric forms of NptbH, as well as for its dimeric complex, have been calculated, using density functional B3LYP method involving several basis sets and the results were compared with the experimental values. Conformational studies have been also carried out regarding its tautomeric monomer forms as well as the dimer form. According to all calculations the thione form of NptbH (II) is about 41.2- 75.3 kJ/mol more stable than the thiol form (I) and the dimeric conformation (III) predicted to be more stable than the monomeric conformations (I) and (II). Vibrational assignments have been made, and it is found that the calculated normal mode frequencies of dimeric (III) and monomeric (II) molecules are required for the analysis of IR and Raman spectra of the NptbH in the solid and solution states. The i...
1,1,1,3,3,3-Hexachloroacetone (HCA) is used in synthesis of many organic compounds [1-10] and its... more 1,1,1,3,3,3-Hexachloroacetone (HCA) is used in synthesis of many organic compounds [1-10] and its main use is as pesticide [11-15]. The structure of HCA has been studied by gas phase electron diffraction, GED, technique [16,17]. Andersen et al. [17] according to their GED study, concluded a C1 symmetry point group for HCA molecule with two different ClCCO dihedral angles of 16.9o and 39.5o. However, Johansen et al. [16] concluded a C2 structure for HCA with ClCCO dihedral angle of 31.6o. According to the Johansen et al. [16] results, the C=O, C-C, and CCl bond lengths are 1.184, 1.574, 1.764 Å, respectively. The measurements of dipole moments in the CCl4 solution and as neat liquid of HCA give 1.24 and 1.34 Debye, respectively [18]. The energy of C2 structure was 5.17 kcal/mol lower than the theoretical C2v structure, calculated at the MP2/6-311+G(2d) level [16]. To the best of our knowledge, there is no report on the vibrational spectra of HCA in literature. Therefore, this study h...
Fourier transform infrared and Fourier transform Raman spectra of 3,4-diacetyl-2,5-hexanedione, k... more Fourier transform infrared and Fourier transform Raman spectra of 3,4-diacetyl-2,5-hexanedione, known as tetraacetylethane (TAE) or a,a 0-bis-acetylacetone, and its deuterated analogue have been obtained. Density functional theory (DFT) B3LYP and BLYP calculations have been carried out with the purpose of understanding the vibrational spectra of this compound and its deuterated analogue. The calculated geometrical parameters show a very strong hydrogen bond, compared with its parent molecule, acetylacetone (AA), with an O O distance of 2.464–2.505 Å. This bond length is about 0.05–0.06 Å shorter than that for AA. According to the theoretical calculations, TAE has an asymmetric structure with a hydrogen bond strength of about 17.3 kcal/mol per bond (calculated with 6311++G** basis set), about 1.4 kcal/mol more than that for AA. This increase in the hydrogen bond strength is consistent with the frequency shifts for OH/OD stretching, OH/OD out-of-plane bending, and O O stretching modes...
The stability of two stable cis-enol forms in two categories of β-diketones, including para-subst... more The stability of two stable cis-enol forms in two categories of β-diketones, including para-substituted of trifluorobenzoylacetone (X-TFBA) and 1-aryl-1,3-diketone malonates (X-ADM, X: H, NO2, OCH3, CH3, OH, CF3, F, Cl, and NH2) has been obtained by different theoretical methods. According to our results, the energy difference between the mentioned stable chelated enol forms for the titled compounds is negligible. The theoretical equilibrium constants between the two stable cis-enol of the mentioned molecules are in excellent agreement with the reported experimental equilibrium constant. In addition, the effect of different substitutions on the intramolecular hydrogen bond strength has been evaluated. The correlation between Hammett para-substituent constants, σp. with the theoretical and experimental parameters related to the strength of hydrogen bond in p-X-TFBA and p-X-ADM molecules also investigated by means of density functional theory calculations. The electronic effects of pa...
In this work, the mechanism of the palladium-catalysed acetoxylation of benzene C-H has been stud... more In this work, the mechanism of the palladium-catalysed acetoxylation of benzene C-H has been studied theoretically in detail. Based on experimental studies, a four-step mechanism for this reaction had been proposed, that is, C−H activation of benzene is the rate-determining step which forms an intermediate ( k1 pathway) which is subsequently oxidized to produce a high-valent Pd intermediate ( k2 pathway). Using quantum chemical calculations, all pathways were investigated, and the activation energy, activation enthalpy and activation Gibbs free energy for all steps were calculated and compared with each other. It was determined that the RDS proceeds through a square complex instead of a T-shaped complex. The activation energy related to the k2 pathway is higher than that of the RDS, and therefore, a new mechanism is proposed.
ABSTRACT The geometry of calcium acetylacetonate, Ca(acac)2, has been optimized at the B3LYP leve... more ABSTRACT The geometry of calcium acetylacetonate, Ca(acac)2, has been optimized at the B3LYP level, using 6-311G* and 6-311++G** basis sets. The vibrational frequencies and potential energy distribution (PED) of the internal coordinates were calculated at the B3LYP/6-311++G** level. The calculated vibrational frequencies were compared with the FT-IR and FT-Raman band frequencies. Excellent agreement was observed between theoretical and experimental results. The geometries and vibrational frequencies of Ca(acac)2 were compared with the corresponding values of beryllium and magnesium acetylacetonates, Be(acac)2 and Mg(acac)2.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2018
An interpretation of the experimental IR and Raman spectra of Aluminum (III) trifluoroacetylaceto... more An interpretation of the experimental IR and Raman spectra of Aluminum (III) trifluoroacetylacetonate (Al(TFAA)3) complex, which were synthesized by us, is first reported here. The charge distribution, isomerism, strength of metal‑oxygen binding and vibrational spectral properties for this complex structure were theoretically investigated through population analysis, geometry optimization and harmonic frequency calculations, performed at B3LYP/6-311G* level of theory. In the population analysis, two different approaches reffered to as "Atoms in molecules (AIM)", and "Natural Bond Orbital (NBO)" were used. According to the calculation resuls, the energy difference between the cis and trans isomers of Al(TFAA)3 is very small and indicates that both isomers coexist in the sample in comparable proportions. Comparison of the calculated frequency and intensity data with the observed IR and Raman spectra of the complex has supported this conclusion. On the other hand, comparison of the structural and vibrational spectral data of Al(TFAA)3, which were experimentally measured and calculated at B3LYP/6-311G* level, with the corresponding data of Aluminum acetylacetonate (Al(AA)3) has revealed the effects of CF3 substitution on the structural and vibrational spectral data associated with the CH3 groups in the complex structure.
Molecular structure and vibrational spectra of acetone, acetone-d3, and acetone-d6 were investiga... more Molecular structure and vibrational spectra of acetone, acetone-d3, and acetone-d6 were investigated by means of ab initio and density functional theory (DFT) calculations. The harmonic and anharmonic vibrational frequencies of the acetone isotopomers were calculated at the B3LYP (using the 6–311++G(3df,3pd) basis set) and B2PLYP (using the 6–31+(2d,p) and 6–311G(2df,p) basis sets) levels. The calculated frequencies and the Raman and infrared (IR) intensities were compared with the experimental results. Excellent agreement between calculated and observed vibrational wavenumbers was obtained. Additionally, a normal coordinate analysis (NCA) was also done by using the normal mode eigenvectors obtained at the B3LYP/6–311++G(3df,3pd) level. All fundamental vibrational bands were assigned to the normal modes with the aid of the potential energy distribution (PED) values obtained from normal coordinate calculations. To study the internal rotation of CH3 groups, single CH3 rotation and syn...
FTIR and Raman spectra of an anti-bacterial compound, N-phenylthiobenzamide (NptbH), were recorde... more FTIR and Raman spectra of an anti-bacterial compound, N-phenylthiobenzamide (NptbH), were recorded in the solid phase and in solution. The harmonic vibration wavenumbers, for both the tautomeric forms of NptbH, as well as for its dimeric complex, have been calculated, using density functional B3LYP method involving several basis sets and the results were compared with the experimental values. Conformational studies have been also carried out regarding its tautomeric monomer forms as well as the dimer form. According to all calculations the thione form of NptbH (II) is about 41.2- 75.3 kJ/mol more stable than the thiol form (I) and the dimeric conformation (III) predicted to be more stable than the monomeric conformations (I) and (II). Vibrational assignments have been made, and it is found that the calculated normal mode frequencies of dimeric (III) and monomeric (II) molecules are required for the analysis of IR and Raman spectra of the NptbH in the solid and solution states. The i...
1,1,1,3,3,3-Hexachloroacetone (HCA) is used in synthesis of many organic compounds [1-10] and its... more 1,1,1,3,3,3-Hexachloroacetone (HCA) is used in synthesis of many organic compounds [1-10] and its main use is as pesticide [11-15]. The structure of HCA has been studied by gas phase electron diffraction, GED, technique [16,17]. Andersen et al. [17] according to their GED study, concluded a C1 symmetry point group for HCA molecule with two different ClCCO dihedral angles of 16.9o and 39.5o. However, Johansen et al. [16] concluded a C2 structure for HCA with ClCCO dihedral angle of 31.6o. According to the Johansen et al. [16] results, the C=O, C-C, and CCl bond lengths are 1.184, 1.574, 1.764 Å, respectively. The measurements of dipole moments in the CCl4 solution and as neat liquid of HCA give 1.24 and 1.34 Debye, respectively [18]. The energy of C2 structure was 5.17 kcal/mol lower than the theoretical C2v structure, calculated at the MP2/6-311+G(2d) level [16]. To the best of our knowledge, there is no report on the vibrational spectra of HCA in literature. Therefore, this study h...
Fourier transform infrared and Fourier transform Raman spectra of 3,4-diacetyl-2,5-hexanedione, k... more Fourier transform infrared and Fourier transform Raman spectra of 3,4-diacetyl-2,5-hexanedione, known as tetraacetylethane (TAE) or a,a 0-bis-acetylacetone, and its deuterated analogue have been obtained. Density functional theory (DFT) B3LYP and BLYP calculations have been carried out with the purpose of understanding the vibrational spectra of this compound and its deuterated analogue. The calculated geometrical parameters show a very strong hydrogen bond, compared with its parent molecule, acetylacetone (AA), with an O O distance of 2.464–2.505 Å. This bond length is about 0.05–0.06 Å shorter than that for AA. According to the theoretical calculations, TAE has an asymmetric structure with a hydrogen bond strength of about 17.3 kcal/mol per bond (calculated with 6311++G** basis set), about 1.4 kcal/mol more than that for AA. This increase in the hydrogen bond strength is consistent with the frequency shifts for OH/OD stretching, OH/OD out-of-plane bending, and O O stretching modes...
The stability of two stable cis-enol forms in two categories of β-diketones, including para-subst... more The stability of two stable cis-enol forms in two categories of β-diketones, including para-substituted of trifluorobenzoylacetone (X-TFBA) and 1-aryl-1,3-diketone malonates (X-ADM, X: H, NO2, OCH3, CH3, OH, CF3, F, Cl, and NH2) has been obtained by different theoretical methods. According to our results, the energy difference between the mentioned stable chelated enol forms for the titled compounds is negligible. The theoretical equilibrium constants between the two stable cis-enol of the mentioned molecules are in excellent agreement with the reported experimental equilibrium constant. In addition, the effect of different substitutions on the intramolecular hydrogen bond strength has been evaluated. The correlation between Hammett para-substituent constants, σp. with the theoretical and experimental parameters related to the strength of hydrogen bond in p-X-TFBA and p-X-ADM molecules also investigated by means of density functional theory calculations. The electronic effects of pa...
In this work, the mechanism of the palladium-catalysed acetoxylation of benzene C-H has been stud... more In this work, the mechanism of the palladium-catalysed acetoxylation of benzene C-H has been studied theoretically in detail. Based on experimental studies, a four-step mechanism for this reaction had been proposed, that is, C−H activation of benzene is the rate-determining step which forms an intermediate ( k1 pathway) which is subsequently oxidized to produce a high-valent Pd intermediate ( k2 pathway). Using quantum chemical calculations, all pathways were investigated, and the activation energy, activation enthalpy and activation Gibbs free energy for all steps were calculated and compared with each other. It was determined that the RDS proceeds through a square complex instead of a T-shaped complex. The activation energy related to the k2 pathway is higher than that of the RDS, and therefore, a new mechanism is proposed.
ABSTRACT The geometry of calcium acetylacetonate, Ca(acac)2, has been optimized at the B3LYP leve... more ABSTRACT The geometry of calcium acetylacetonate, Ca(acac)2, has been optimized at the B3LYP level, using 6-311G* and 6-311++G** basis sets. The vibrational frequencies and potential energy distribution (PED) of the internal coordinates were calculated at the B3LYP/6-311++G** level. The calculated vibrational frequencies were compared with the FT-IR and FT-Raman band frequencies. Excellent agreement was observed between theoretical and experimental results. The geometries and vibrational frequencies of Ca(acac)2 were compared with the corresponding values of beryllium and magnesium acetylacetonates, Be(acac)2 and Mg(acac)2.
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