Y. Erdogdu

DFT-based molecular modeling, NBO analysis and vibrational spectroscopic study of 3-(bromoacetyl)coumarin.

The NIR-FT Raman and FT-IR spectra of 3-(bromoacetyl)coumarin (BAC) molecule have been recorded and analyzed. Density functional theory (DFT) calculation of two BAC conformers has been performed to find the optimized structures and computed vibrational wavenumbers of the most stable one. The obtained vibrational wavenumbers and optimized geometric parameters were seen to be in good agreement with the experimental data. Characteristic vibrational bands of the pyrone ring and methylene and carbonyl groups have been identified. The lowering of HOMO-LUMO energy gap clearly explains the charge transfer interactions taking place within the molecule.

Analysis of vibrational spectra of 2 and 3-methylpiperidine based on density functional theory calculations

The experimental and theoretical vibrational spectra of 2 and 3-methylpiperidine (abbreviated as 2-MP and 3-MP) were studied. The FT-Infrared spectra of 2-MP and 3-MP molecules were recorded in the liquid phase. The structural and spectroscopic analysis of the title molecules were made by using density functional harmonic calculations. For the title molecules, only one form was found most stable structure by using B3LYP level with the 6-311G (d,p) basis set. Selected experimental bands were assigned and characterized based on the scaled theoretical wave numbers by their total energy distribution (TED).

FT-Raman, FT-IR spectra and total energy distribution of 3-pentyl-2,6-diphenylpiperidin-4-one: DFT method

FT-Raman and FT-IR spectra were recorded for 3-pentyl-2,6-diphenylpiperidin-4-one (PDPO) sample in solid state. The equilibrium geometries, harmonic vibrational frequencies, infrared and the Raman scattering intensities were computed using DFT/6-31G(d,p) level. Results obtained at this level of theory were used for a detailed interpretation of the infrared and Raman spectra, based on the total energy distribution (TED) of the normal modes. Molecular parameters such as bond lengths, bond angles and dihedral angles were calculated and compared with X-ray diffraction data. This comparison was good agreement. The intra-molecular charge transfer was calculated by means of natural bond orbital analysis (NBO). Hyperconjugative interaction energy was more during the π-π* transition. Energy gap of the molecule was found using HOMO and LUMO calculation, hence the less band gap, which seems to be more stable. Atomic charges of the carbon, nitrogen and oxygen were calculated using same level of calculation.

Structural conformations and vibrational spectral study of chloroflavone with density functional theoretical simulations.

NIR-FT Raman and FT-IR spectra of 6-chloroflavone were recorded and analyzed. The vibrational wavenumber of the compound have been computed using B3LYP/6-31++G(d,p) level to derive the equilibrium geometry, conformational stability, molecular orbital energies and vibrational wavenumbers. The carbonyl stretching vibrations have been lowered due to conjugation and hydrogen bonding in the molecules. The assignment of fundamental vibrations agrees well with the calculated wavenumbers.

Structural, vibrational and hyperpolarizability calculation of (E)-2-(2-hydroxybenzylideneamino)-3-methylbutanoic acid.

The (E)-2-(2-hydroxybenzylideneamino)-3-methylbutanoic acid (E)-2HBAMBA was synthesized. The FT-IR, FT-Raman and UV-vis spectra have been recorded and characterized. Theoretical wavenumbers along with IR and Raman intensities were calculated using B3LYP/6-31G(d,p) level and total energy distribution (TED) of the various normal mode of vibrations were also studied. The conformational analysis was performed for a stable conformer by selecting the dihedral angles and the optimized bond parameters were calculated for the stable structure. Effect of intramolecular interactions is calculated by changing the orientation of hydroxyl hydrogen. To know the charge transfer while changing the hydroxyl group hydrogen orientation, the NBO analysis was performed. Using the same level of calculation, the electronic charge transfers were calculated and compared.

FT-Raman, FT-IR spectral and DFT studies on (E)-1-4-nitrobenzylidenethiocarbonohydrazide

Quantum mechanical calculation of optimized parameters, vibrational wavenumbers and energies of (E)-1-4-nitrobenzylidenethiocarbonohydrazide ((E)-1-4-NBTCH) was carried out using Hatree Fock (HF) with 6-31G(d,p), 6-311G(d,p) basis sets and density functional theory (DFT) with 6-31G(d,p) basis set. The optimized geometrical parameters obtained by HF and DFT are in better agreement with analogues single XRD data. The vibrational wavenumbers were calculated and the complete assignments were performed on the basis of total energy distribution (TED), calculated with scaled quantum mechanical (SQM) method. The electrical dipole moment (μ) and first hyperpolarizability (β(0)) values have been computed using ab initio and DFT quantum mechanical calculation. The calculated results (β(0)) show that the title molecule might have nonlinear optical (NLO) behaviour. The total energy, dipole moment and rotational constant are reported for the title molecule. The HOMO-LUMO energies were calculated and natural bonding orbital (NBO) analysis has also been carried out.

Synthesis and spectral characterization of hydrazone derivative of furfural using experimental and DFT methods.

The Spectral Characterization of (E)-1-(Furan-2-yl) methylene)-2-(1-phenylvinyl) hydrazine (FMPVH) were carried out by using FT-IR, FT-Raman and UV-Vis., Spectrometry. The B3LYP/6-311++G(d,p) level of optimization has been performed on the title compound. The conformational analysis was performed for this molecule, in which the cis and trans conformers were studied for spectral characterization. The recorded spectral results were compared with calculated results. The optimized bond parameters of FMPVH molecule was compared with X-ray diffraction data of related molecule. To study the intra-molecular charge transfers within the molecule the Lewis (bonding) and Non-Lewis (anti-bonding) structural calculation was performed. The Non-linear optical behavior of the title compound was measured using first order hyperpolarizability calculation. The atomic charges were calculated and analyzed.

Vibrational spectra, structural conformations, scaled quantum chemical calculations and NBO analysis of 3-acetyl-7-methoxycoumarin.

The powder form NIR-FT Raman and FT-IR spectra of 3-acetyl-7-methoxycoumarin (3A7MC) have been recorded in the regions 4000-400 and 3500-100 cm(-1), respectively. The equilibrium geometry, vibrational frequencies, band intensities, NMR spectra, NBO analysis and UV-Vis spectral studies of the most stable conformer have been calculated by density functional B3LYP method with the 6-311G(d,p) basis set. A complete vibrational analysis has been attempted on the basis of experimental infrared and Raman spectra, the calculated wavenumber and intensity of the vibrational bands and the potential energy distribution over the internal coordinates. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping the electron density isosurface with electrostatic potential surfaces (ESP). Natural bond orbital analysis has been carried out to understand the nature of different interactions responsible for the electron delocalization and the intramolecular charge transfer between the orbitals (n→π(∗), n→σ(∗), π→π(∗)).

FT-IR, FT-Raman spectral and conformational studies on (E)-2-(2-hydroxybenzylidenamino)-3-(1H-indol-3yl) propionic acid

The (E)-2-(2-hydroxybenzylidenamino)-3-(1H-indol-3yl) propionic acid ((E)-2HBA3IPA) was synthesized. The theoretical conformational analysis was performed to identify the stable structure. Optimized molecular bond parameters were calculated by using B3LYP/6-31G(d,p) basis set. The hyperconjugative interaction energy (E(2)) and electron densities of donor (i) and acceptor (j) bonds were calculated using NBO analysis. First order hyperpolarizability (β0) was calculated. The band gap energy was analyzed by UV-Visible recorded spectra and compared with theoretical band gap TD-DFT/B3LYP/6-31G(d,p) values. The intra-molecular hydrogen bonding interaction was identified between nitrogen and hydroxyl hydrogen (N⋯H-O).

DFT simulations, FT-IR, FT-raman, and FT-NMR spectra of 4-(4-chlorophenyl)-1H-imidazole molecules

The FT-IR, FT-Raman and FT-NMR spectra of the compound 4-(4-Chlorophenyl)-1H-imidazole (4-ClPI) was recorded and analyzed. Density functional method has been used to compute optimized geometry, vibrational wavenumbers and NMR spectra of the 4-ClPI. Only one tautomeric form was found most stable by using B3LYP functional with the 6–311++G(d,p) as basis sets. The detailed interpretation of the vibrational spectra was carried out with the aid of total energy distribution (TED) following the scaled quantum mechanical force field methodology.