Conformational analysis, tautomerization, IR, Raman, and NMR studies of benzyl acetoacetate (original) (raw)
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Molecular structure and vibrational assignment of dimethyl oxaloacetate
Journal of Molecular Structure, 2004
A complete conformational analysis of the keto and chelated enol forms of dimethyl oxaloacetate (DMOA), a β-dicarbonyl compound, was carried out by ab initio calculations, at the density functional theory (DFT) level. In addition to nine stable enol conformers, which are stabilized by intramolecular hydrogen bonds, twelve stable keto conformers were also obtained. The considerably higher energy of the keto compared to that of the most stable enol conformer makes the presence of keto form, at least in the gas phase, unlikely.Theoretical calculations in the solution, using the Onsager Method, suggest two coexisting enol conformers in the solution. This finding is in agreement with the experimental data.The hydrogen bond strength of the most stable conformer of DMOA is compared with that of acetylacetone (AA). Harmonic vibrational frequencies of this stable enol form and its deuterated analog were also calculated and compared with the experimental data. According to the theoretical calculations, the enolated proton in dimethyl oxaloacetate moves in an asymmetric single minimum potential with a hydrogen bond strength of 31.1 kJ/mol, 35.3 kJ/mol less than that of AA. This weakening of hydrogen bond is consistent with the frequency shifts for OH/OD stretching, OH/OD out-of-plane bending and O⋯O stretching modes. The calculated O⋯O distance is about 0.07–0.08 Å longer than that of its parent AA.
The Journal of Organic Chemistry, 2006
Results of MP2 calculations with 6-31G(d,p) basis sets: cartesian coordinates, electronic energies, number of imaginary frequencies, zero point corrections, thermal corrections to Energies, Enthalpies and Gibbs Free Energies for enol and diketo confomers. S2 Results of B3LYP calculations with 6-31G(d,p) basis sets: cartesian coordinates, electronic energies, number of imaginary frequencies, zero point corrections, thermal corrections to Energies, Enthalpies and Gibbs Free Energies for enol and diketo confomers. S3 Results of MP2 calculations with 6-311++G(3df,pd) basis sets: cartesian coordinates, electronic energies, number of imaginary frequencies, zero point corrections, thermal corrections to Energies, Enthalpies and Gibbs Free Energies for enol and diketo confomers. S4 Results of B3LYP calculations with 6-311++G(3df,pd) basis sets: cartesian coordinates, electronic energies, number of imaginary frequencies, zero point corrections, thermal corrections to Energies, Enthalpies and Gibbs Free Energies for enol and diketo confomers.
Oriental Journal of Chemistry, 2017
Conformational stability, equilibrium constant between two stable cis-enol forms, and intramolecular hydrogen bonding (IHB) of benzoylacetone (BA) and p-substituted benzoylacetone (X-BA), where X=NO 2 , OCH 3 , CH 3 , OH, CF 3 , Cl, F, and NH 2 , have been investigated by means of density functional theory (DFT) calculations and compared with the reported experimental results. According to our calculations, the energy difference between the two stable chelated enol forms is negligible, about 0.35-1.1 kcal/mol ranges in the gas phase and different solvents. The electronic effects of p-substituted benzoylacetone on IHB strength were determined and established by NMR, IR spectra, geometry, and topological parameters with Hammett linear free energy relationships. Also, the linear correlation coefficients between σ p and selected parameters related to IHB strength, such as geometrical, topological parameters, IR and NMR spectroscopic data, and NBO results related to IHBs were considered. Good linear correlations between σ p and the mentioned parameters were obtained
Journal of Molecular Structure-theochem, 2008
The molecular structure of 3-(phenylthio)pentane-2,4-dione (PTPD) has been investigated by means of Density Functional Theory (DFT) calculations and the results were compared with those of the unsubstituted parent, pentane-2,4-dione (known as acetylacetone, AA). The harmonic vibrational frequencies of the cis-enol form were calculated at the B3LYP level using 6-31G ** and 6-311G ** basis sets. The calculated frequencies and the Raman and IR intensities were compared with the experimental results. The infrared and Raman spectra of PTPD and its deuterated analogue are recorded in the 4000-100 cm À1 range. The observed vibrational wave numbers were analyzed in light of the computed vibrational spectra.
Journal of Molecular Structure, 2011
Complete conformational analyses of all possible keto and enol forms, molecular structure, intramolecular hydrogen bonding (IHB), and vibrational frequencies of 5,5-dimethyl hexane-2,4-dione (DMHD, also known as acetylpinacolin and pivalylacetone), were investigated by means of ab initio calculations and IR and Raman spectroscopies. The results are compared with those of acetylacetone (AA) and 2,2,6,6-tetramethyl-3,5-heptanedione (TMHD). The energy differences between three stable E1, E2, and E3 chelated enol forms are negligible. Comparing the calculated and experimental band frequencies and intensities suggests the coexisting of these three conformers in comparable proportions in the sample. The vibrational frequencies of DMHD and its deuterated analogue were also clearly assigned. According to the theoretical calculations, the stable cis-enol conformers of DMHD have an average hydrogen bond strength of 16.6 kcal/mol, calculated at the B3LYP/6-311++G** level, which is about 0.7 kcal/mol stronger than that of AA. This enhancement in the IHB strength is also consistent with the experimental results of the band frequency shifts of OH/OD and O⋯O stretching and OH/OD out of plane bending frequencies. The theoretical calculations and spectroscopic results indicate that the IHB strength of DMHD is between those of AA and TMHD.► Substitution of bulky groups (such as t-butyl) in the β-positions of acetylacetone increases the enol content in the sample. ► Both theoretical and experimental data indicate that the hydrogen bond in DMHD is stronger than that in acetylacetone. ► More than one enol conformer exists in the sample.
Journal of Molecular Structure-theochem, 2008
The molecular structure of 3-(phenylthio)pentane-2,4-dione (PTPD) has been investigated by means of Density Functional Theory (DFT) calculations and the results were compared with those of the unsubstituted parent, pentane-2,4-dione (known as acetylacetone, AA). The harmonic vibrational frequencies of the cis-enol form were calculated at the B3LYP level using 6-31G∗∗ and 6-311G∗∗ basis sets. The calculated frequencies and the Raman and IR intensities were compared with the experimental results. The infrared and Raman spectra of PTPD and its deuterated analogue are recorded in the 4000–100 cm−1 range. The observed vibrational wave numbers were analyzed in light of the computed vibrational spectra.According to the theoretical calculations, the hydrogen bond strength for PTPD is 6.1–6.8 kJ/mol stronger than in AA. This result is in agreement with the OH/OD stretching, OH/OD in-plane bending, O···O stretching frequencies, and NMR chemical shift data.Natural Bond Orbital (NBO) analyses indicate that both steric and resonance effects are responsible for increasing the hydrogen bond strength in PTPD.
Hydrogen bonding in acetylacetaldehyde: Theoretical insights from the theory of atoms in molecules
International Journal of Quantum Chemistry, 2009
All the possible conformations of tautomeric structures (keto and enol) of acetylacetaldehyde (AAD) were fully optimized at HF, B3LYP, and MP2 levels with 6-31G(d,p) and 6-311ϩϩG(d,p) basis sets to determine the conformational equilibrium. Theoretical results show that two chelated enol forms have extra stability with respect to the other conformers, but identification of global minimum is very difficult. The high level ab initio calculations G2(MP2) and CBS-QB3) also support the HF conclusion. It seems that the chelated enol forms have equal stability, and the energy gap between them is probably lies in the computational error range. Finally, the analysis of hydrogen bond in these molecules by quantum theory of atoms in molecules (AIM) and natural bond orbital (NBO) methods fairly support the ab initio results.
Structure and vibrational assignment of the enol form of 3-chloro-pentane-2,4-dione
Journal of Molecular Structure, 2008
Molecular structure of 1-chloro-1,1-difluoro-pentane-2,4-dione (monochlorodifluoro-acetylacetone, CDFAA) has been investigated by means of ab initio and Density Functional Theory (DFT) calculations and the results were compared with those of 1,1,1-trifluoropentane-2,4-dione (trifluoro-acetylacetone, TFAA). The harmonic vibrational frequencies of the two most stable cis-enol forms were calculated at the B3LYP level of theory using 6-31G ** and 6-311++G ** basis sets. We also calculated the anharmonic frequencies at the B3LYP/6-31G ** level of theory for these two stable cis-enol isomers. The calculated frequencies and the Raman and IR intensities were compared with the experimental results. The energy difference between the two stable cis-enol forms, calculated at the MP2/6-31G ** level, is only 3.42 kJ/mol. The observed vibrational frequencies and intensities in the gas phase are in excellent agreement with the corresponding values calculated for the two most stable conformers. However, the observed IR and Raman frequencies also indicate coexisting of both tautomers in the liquid phase and in solution. According to the theoretical calculations, at the B3LYP/6-311++G ** level, the hydrogen bond strength for the most stable conformer is 54.45 kJ/mol, about 2.4 kJ/mol less than that of the corresponding conformer of TFAA. These results are in agreement with the obtained experimental data.
Intramolecular hydrogen bond, molecular structure and vibrational assignment of tetra-acetylethane
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2006
The intramolecular hydrogen bond, molecular structure and vibrational frequencies of tetra-acetylethane have been investigated by means of high-level density functional theory (DFT) methods with most popular basis sets. Fourier transform infrared and Fourier transform Raman spectra of this compound and its deuterated analogue were recorded in the regions 400-4000 cm −1 and 40-4000 cm −1 , respectively. The calculated geometrical parameters of tetra-acetylethane were compared to the experimental results of this compound and its parent molecule (acetylacetone), obtained from X-ray diffraction. The O•••O distance in tetra-acetylethane, about 2.424Å, suggests that the hydrogen bond in this compound is stronger than acetylacetone. This conclusion is well supported by the NMR proton chemical shifts and O-H stretching mode at 2626 cm −1. Furthermore, the calculated hydrogen bond energy in the title compound is 17.22 kcal/mol, which is greater than the acetylacetone value. On the other hand, the results of theoretical calculations show that the bulky substitution in ␣-position of acetylacetone results in an increase of the conjugation of electrons in the chelate ring. Finally, we applied the atoms in molecules (AIM) theory and natural bond orbital method (NBO) for detail analyzing the hydrogen bond in tetra-acetylethane and acetylacetone. These results are in agreement with the vibrational spectra interpretation and quantum chemical calculation results. Also, the conformations of methyl groups with respect to the plane of the molecule and with respect to each other were investigated.