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    Combined spectroscopic, XRD crystal structure and DFT studies on 2-(ethylthio)pyrimidine-4,6-diamine
    (Elsevier, 2017) Aktan, Ebru; Babur, Banu; Seferoglu, Nurgul; Catikkas, Berna; Kaynak, F. Betul; Seferoglu, Zeynel
    In this study, the compound 2-(ethylthio)pyrimidine-4,6-diamine (ETPD) was re-synthesized and its single crystals were obtained by slow evaporation of ethanol solution. The characterization of the molecule was done experimentally and theoretically. The single-crystal X-ray diffraction analysis shows that ETPD crystallizes in the orthorhombic space group P2(1)2(1)2(1). The ground state geometry, vibrational spectra, NMR spectra, frontier molecular orbitals and also the map of molecular electrostatic potential (MEP) of ETPD obtained using DFT calculations were evaluated in detail. In addition, the global reactivity descriptors were obtained within the frontier molecular orbitals calculations. The comparison of the DFT results obtained by different methods and basis sets with X-ray diffraction analysis display the DFT can well reproduce the structure of the compound. (C) 2017 Elsevier B.V. All rights reserved.
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    DFT, FT-Raman, FTIR, NMR, and UV-Vis studies of a hetarylazo indole dye
    (Wiley, 2013) Catikkas, Berna; Aktan, Ebru; Seferoglu, Zeynel
    In this study, computational calculations of 1,2-dimethyl-3-[(5-methylsulfanyl-1,3,4-thiadiazol-2-yl)diazenyl]-1H-indole have been carried out using the Becke-3-LeeYangParr density functional methods with 6-311+G(d,p) basis set. The geometry optimization and fundamental frequencies of the most stable configuration have been calculated. The FTIR and FT-Raman spectra of the compound have been recorded and compared to the calculated frequency values. The total energy distribution of the fundamental modes has been obtained using scaled quantum mechanical program. The 1H NMR chemical shifts have been calculated using the gauge-independent atomic orbital approach. The theoretical electronic absorption spectra have been calculated using time-dependent density functional theory. The conductor-like screening solvation model has been applied to calculate the chemical shifts and maximum absorption wavelength values. The calculated values have been compared with the corresponding experimental results. (C) 2012 Wiley Periodicals, Inc.
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    Infrared and Raman spectra, DFT investigation of the tautomerism, conformational equilibrium, structure and vibrational assignment of 1-(2-benzothiazolyl)-3-methyl pyrazol-5-one
    (Elsevier, 2013) Aktan, Ebru; Catikkas, Berna
    The low energy conformations of the three tautomers, imine-enol, enamine-keto and imine-keto forms of the title compound have been determined at the B3LYP/6-31 + G(d) level of theory using the relaxed PES scan method and their geometries have been refined at B3LYP/6-311 + G(d,p) and PBE0/6-311 + G(d,p) levels. The results show that the title compound exists in the imine-enol tautomeric form, in contrast to the enamine-keto form which exists in the solid crystalline state, followed by enamine-keto and imine-keto forms with extremely low abundances. The geometry parameters of all tautomeric forms calculated at PBE0/6-311 + G(d,p) and B3LYP/6-311 + G(d,p) levels have been compared with those from the experimental X-ray diffraction. The vibrational (FT-IR and Raman) spectroscopic studies of the most stable tautomer, enamine-keto form have been carried out. The assignment of the fundamental bands observed in the IR and Raman spectra have been facilitated by the SQM force field procedure. The frequencies from SQM procedure have a very good fit to the experimental ones. The total root-mean-square error is only ca. 11 cm(-1). (C) 2013 Elsevier B.V. All rights reserved.
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    Vibrational and electronic investigations, NLO, FMO analysis on a hetarylazoindole disperse dye by density functional theory
    (Elsevier, 2016) Catikkas, Berna; Aktan, Ebru; Yalcin, Ergin
    This work deals with the optimized molecular structure, vibrational spectra, nonlinear optic (NLO) and frontier molecule orbital (FMO) properties of 1-Methy1-2-pheny1-3-(1,3,4-thiadiazol-2-yldiazeny1)-1Hindole (MPI) by quantum chemical calculations. The Fourier transform infrared (Fr-MIR and Fr-FIR) and Raman spectra of 1-Methyl-2-phenyl-3-(1,3,4-thiadiazol-2-yldiazenyl)-1H-indole (MPI) were recorded in the region (4000-400 cm(-1) and 400-30 cm(-1)) and (3200-92 cm(-1)), respectively. The analysis and complete vibrational assignments of the fundamental modes of the MPI molecule were carried out by using the observed Fr-IR and Fr-Raman data and calculated Total Energy Distribution (TED) according to Scaled Quantum Mechanics procedure. The calculated geometrical parameters of the MPI molecule are in agreement with the obtained values from XRD studies. On the other hand, the difference between the scaled and observed wavenumber values of the most of the fundamentals are very sma11.1H NMR and 13C NMR chemical shift values, and energy gap between LUMO-HOMO and molecular electrostatic potential (MEP) were investigated by using density functional theory (B3LYP) methods. UV/Visible spectra and X maximum absorption values, the oscillator strengths in the chloroform, methanol and DMSO solvation in combination with different basis sets were calculated by using the time-dependent density functional theory (1D-DFT). Additionally, the predicted nonlinear optical (NLO) properties of the MPI are quite greater than that of urea at the B3LYP/6-31++G(d,p) level. (C) 2016 Elsevier B.V. All rights reserved.