Serdar Badoğlu

FTIR, Raman and NMR spectroscopic and DFT theoretical studies on poly(N-vinylimidazole).

In this study where the FTIR, Raman, (1)H NMR and (13)C NMR spectra of poly(N-vinylimidazole) which can be abbreviated as poly(NVIM) are first reported, a comparison of the experimental and theoretical vibrational spectral data of monomer NVIM and water-soluble poly(NVIM) has been given; such a comparison over the vibrational modes and associated spectral data calculated at B3LYP/6-31+G(d) level of theory for NVIM and its stable dimer forms provided significant contributions for getting a reliable interpretation of the observed vibrational spectra of poly(NVIM). The obtained results revealed that the change from NVIM to poly(NVIM) should be characterized by the disappearance of the CH₂CH bonds of the vinyl group and the appearance of the aliphatic CH and CH₂ bonds. Besides this, the thermal properties of poly(NVIM) were elucidated by thermogravimetric analyses such as TGA, DTA and DSC, while some electronic structure parameters of the most stable dimers of NVIM were investigated through the structure calculations performed by using B3LYP method and 6-31+G(d) basis set within the density functional theory (DFT) methodology.

FT-IR and FT-Raman spectroscopic and DFT theoretical studies on 4-azabenzimidazole.

The Becke, three-parameter, Lee-Yang-Parr exchange-correlation functional have been used to study the geometry, relative energy, frequency and intensity of the vibrational bands of the 4-azabenzimidazole (4AB) tautomers and the most stable tautomers homodimers. FT-IR and Raman spectra of the 4AB have been measured in the regions 4000-100 cm(-1) and 3500-100 cm(-1), respectively for the first time. The stability of 4AB tautomers were reported. All vibrational frequencies assigned in detail with the help of total energy distribution (TED) and isotopic shifts. The energy and atomic charges were discussed. NH⋯N type intermolecular hydrogen bonding interactions were suggested for 4AB dimeric forms. 1H and 13C NMR properties have been calculated for the most stable two tautomeric forms using the gauge independent atomic orbital (GIAO) method.

A study of the molecular structure and spectroscopic properties of 3-hydroxy-2-quinoxalinecarboxylic acid by experimental methods and quantum chemical calculations.

The mid-IR and Raman spectra of 3-hydroxy-2-quinoxalinecarboxylic acid (3HQC) were recorded. These spectra were interpreted with the help of B3LYP/6-311++G(d,p) calculations and potential energy distribution (PED) analysis. As a result of the calculations, seven tautomers were determined among many stable conformations. The experimental spectra were concordant with the theoretical data of two tautomers. In the functional group region overtone and combination bands were detected and assigned. In addition, because of several peaks in the IR spectrum, it was proposed that the 3HQC exhibits dimerization in condensed phase. Possible dimeric forms of 3HQC were evaluated at the same level of theory, and it has been seen that the calculation results confirm the above proposal. 1H and 13C NMR chemical shifts of 3HQC have been calculated, and compared with the experimental data. The frontier molecular orbital properties and the atomic charges were also theoretically obtained and presented.

An experimental and theoretical investigation of free Oxazole in conjunction with the DFT analysis of Oxazole ⋯(H2O)n complexes

The mid-IR spectrum of Oxazole (Oxa) is recorded. This spectrum is interpreted with the help of B3LYP/6-311++G(d,p) calculations and potential energy distribution (PED) analysis. The experimental spectrum is concordant with the theoretical data. Geometrical parameters and the atomic charges are also theoretically obtained and presented. Solvent effects on the geometrical parameters, vibrational frequencies, and electronic properties of Oxa are analyzed theoretically in chloroform, ethanol, and water. Besides, hydrogen bonded Oxa⋯(H2O)n (n=1, 2,…, 10) complexes are investigated within the PCM solvation model. It is found that the interaction energies in Oxa⋯(H2O)n complexes are influenced by the number of water molecules, and by the arrangement of water molecules.

An FT-IR and DFT study of the free and solvated 4-(imidazol-1-yl)phenol

In this study, FT-IR spectrum of 4-(imidazol-1-yl)phenol was recorded. Its vibrational frequencies and modes were determined. Vibrational assignments were proposed with the help of B3LYP/6-311++G(d,p) level of calculations. Three possible dimeric forms of the molecule were investigated theoretically. Besides, solvent effects on the structure, vibrational frequencies, and atomic charges were studied theoretically. Water, dimethyl sulfoxide, and ethanol were the solvents considered. Experimental FT-IR spectrum in DMSO solution was recorded and compared with solid phase experimental data. DFT B3LYP combined with polarized continuum model (PCM) was employed to characterize the solvent effects.

Experimental and theoretical study on free 5-nitroquinoline, 5-nitroisoquinoline, and their zinc(II) halide complexes

In this study where the interpretations of the experimental IR and Raman spectra recorded at room temperature for the ligands 5-nitroquinoline (5NQ) and 5-nitroisoquinoline (5NIQ) and also for their Zn(II) halide (halogen: chlorine, bromine, iodine) complexes were first reported, the assignments of the observed fundamental bands were achieved in the light of the vibrational spectral data and total energy distribution (TED) values calculated at B3LYP/6-311++G(d,p) and B3LYP/LANL2DZ levels of theory. The equilibrium geometrical parameters, Natural Bond Orbital (NBO) charges and frontier orbital (HOMO, LUMO) energies of these molecular structures were also calculated at the same level of theory. Comparisons over the corresponding experimental and theoretical data obtained for the title ligands and their complexes revealed that in complex form both ligands bond to Zn(II) ion through their ring nitrogen atoms and NO2 groups at the same time.

FT-IR spectroscopic and DFT computational study on solvent effects on 8-hydroxy-2-quinolinecarboxylic acid

Solvent effects on the spectroscopic, structural, and electronic properties of 8-hydroxy-2-quinolinecarboxylic acid (8HQC) were analyzed theoretically and experimentally. Density functional theory (DFT) B3LYP/6-311++G(d, p) used within polarized continuum model (PCM) to characterize the solvent effects in benzene, diethyl ether, ethanol, and water. Experimental FT-IR spectra in ethanolic and aqueous solutions were recorded and compared with solid phase experimental data. Nucleus independent chemical shifts were calculated as aromaticity indices. Our results show that the spectroscopic, structural, and electronic properties of 8HQC are solvent dependent.

FT-IR, FT-Raman spectra and quantum mechanical study of piperidine-3-carboxylic acid and its tautomers, isomers

The mid-IR, far-IR, and Raman spectra of piperidine-3-carboxylic acid were measured and interpreted with support of the MP2 and B3LYP/6-311++G(d, p) calculated harmonic vibrational spectra. 10 stable piperidine-3-carboxylic acid tautomers/isomers were found after B3LYP, calculations. The experimental absorption bands of carboxylate (COO−) group show that the free piperidine-3-carboxylic acid molecule exists in zwitterionic form and the most stable tautomer (NAT-1) can be stabilized by an intramolecular N-H...O hydrogen bond. All vibrational frequencies of NAT-1 assigned in detail with the help of total energy distribution (TED). The experimental vibrational wave numbers were compared with the calculated data.

A combined experimental and theoretical study on 8-hydroxy-2-quinolinecarboxylic acid

The mid-IR and Raman spectra of 8-hydroxy-2-quinolinecarboxylic acid (8HQC) were recorded. These spectra were interpreted with the help of B3LYP/6–311 ++G(d,p) calculations and potential energy distribution (PED) analysis. As a result of the calculations, seven tautomers were determined among many stable conformations. The experimental spectra were concordant with the theoretical data of one tautomer. In the functional group region overtone and combination bands were detected and assigned. In addition, because of several peaks in the IR spectrum, it was proposed that the 8HQC exhibits dimerization in condensed phase. Possible dimeric forms of 8HQC were evaluated at the same level of theory, and it has been seen that the calculation results confirm the above proposal. 1H and 13C NMR chemical shifts of 8HQC have been calculated, and compared with the experimental data. The frontier molecular orbital properties and the atomic charges were also theoretically obtained and presented.

XRD, FT-IR, and DFT study on a novel ethyl derivative of 3-hydroxy-2-quinoxalinecarboxylic acid

The novel ethyl derivative of 3-hydroxy-2-quinoxalinecarboxylic acid has been synthesized for the first time, characterized by FT-IR spectroscopy and single-crystal X-Ray diffraction. The crystal packing is achieved by inter-molecular C–H···N, C–H···O and N–H···O type hydrogen bonds, which play an important role in the formation of the 3D supramolecular network of the title compound. The geometries and vibrational frequencies of the title compound in monomer and dimer forms were investigated by density functional theory calculations employing the B3LYP hybrid functional. The calculation results are in accordance with the experimental data. In addition, the theoretical electronic properties like natural bond orbital (NBO) charges and frontier molecular orbitals were presented.