Yazar "Kastas, Cigdem Albayrak" seçeneğine göre listele

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    Analysis of tautomeric equilibrium in (E)-4,6-dibromo-2-[(4-fluorophenylimino)methyl]-3-methoxyphenol compound
    (Pergamon-Elsevier Science Ltd, 2015) Kastas, Cigdem Albayrak; Kastas, Gokhan; Gur, Mahmut; Muglu, Halit; Buyukgungor, Orhan
    In this study, the tautomeric equilibrium between the phenol-imine and keto-amine structural forms of (E)-4,6-dibromo-2-[(4-fluorophenylimino)methyl]-3-methoxyphenol compound has been investigated with experimental (XRD, UV-vis and NMR) and theoretical (DFT and TD-DFT) methods. The results clearly show that structural preference of the compound is definitely depended on its state. Namely, the compound exists in phenol-imine form in the solid state while one or both of these forms can be seen in solvent media. For example, the compound prefers phenol-imine form in benzene while both forms exist in EtOH and DMSO solvents. Coexistence of two forms has been quantified with NMR studies, giving a ratio of 11:9 for phenol and keto structures of the compound in acetone-d(6) solvent. (C) 2015 Elsevier B.V. All rights reserved.
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    CRYSTAL STRUCTURE, SPECTRAL CHARACTERIZATION, MOLECULAR MODELING STUDIES AND STRUCTURAL EFFECTS OF THE PROTON TRANSFER PROCESS FOR (E)-5-METHOXY-2-[(3,4-DIMETHYLPHENYLIMINO)METHYL]PHENOL
    (Soc Chemists Technologists Madeconia, 2017) Kirca, Basak Kosar; Tari, Gonca Ozdemir; Kastas, Cigdem Albayrak; Odabasoglu, Mustafa; Buyukgungor, Orhan
    The main purpose of this study is to characterize a new organic material, (E)-5-methoxy-2-[(3,4-dimethylphenylimino) methyl] phenol, which was synthesized and grown as a single crystal. The molecular structure and spectroscopic properties of the ortho-hydroxy Schiff base compound were determined by X-ray diffraction analysis, Fourier-transform infrared (FT-IR), ultraviolet-visible (UV-Vis) and nuclear magnetic resonance (NMR) spectroscopy techniques, experimentally and computationally with density functional theory (DFT) calculations. X-ray and UV-Vis studies show that the compound exists in an OH tautomeric form in the solid and solvent media. The gas phase geometry optimizations of two possible forms of the title compound, resulting from the prototropic tautomerism, were obtained using DFT calculations at the B3LYP/6-311G+(d,p) level of theory. A relaxed potential energy surface (PES) scan was performed based on the optimized geometry of the OH tautomeric form by varying the redundant internal coordinate, the O-H bond distance. According to the PES scan process, the molecular geometry is strongly affected by the intramolecular proton transfer. The calculated first hyperpolarizability indicates that the compound could be a good material for non-linear optical applications.
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    DEPENDENCE OF TAUTOMERISM ON SUBSTITUENT TYPE IN o-HYDROXY SCHIFF BASES
    (Soc Chemists Technologists Madeconia, 2019) Kastas, Cigdem Albayrak; Kastas, Gokhan
    Quantum computational methods were used to elucidate the structures of the o-hydroxy Schiff bases with different substituents. It is possible for a Schiff base to have different tautomeric structures depending on intramolecular proton transfer from the phenolic oxygen atom to the nitrogen atom. Proton transfer results in two tautomeric structures known as the phenol-imine and keto-amine forms. To explain the substituent effect on the proton transfer process in five o-hydroxy-Schiff bases, possible geometric structures in gas phase were optimized using density functional theory (DFT) at the B3LYP/6-311G(d,p) level. To describe tautomerism including intramolecular proton transfer, potential energy surface (PES) scans were performed starting from the optimized geometry of the phenol-imine form. HOMA indices were calculated in order to estimate pi-electron delocalization. In addition, the substituent effect on the tautomerization rate was examined using Hammett substituent constants and calculating the activation energies.
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    Investigation of molecular structure and solvent/temperature effect on tautomerism in (E)-4,6-dibromo-3-methoxy-2-[(p-tolylimino)methyl] phenol, a new thermochromic Schiff base, by using XRD, FT-IR, UV-vis, NMR and DFT methods
    (Pergamon-Elsevier Science Ltd, 2019) Kastas, Gokhan; Kastas, Cigdem Albayrak; Tabak, Ahmet
    The molecular structure and the solvent temperature effect on the tautomerism in a new Schiff base, (E)-4,6-clibromo-3-methoxy-2-[(p-tolylimino)methyllphenol, were investigated using spectroscopic (NMR, UV-vis, FT-1R), crystallographic (XRD), computational (DFT and TD-DET) methods and harmonic oscillator model of aromaticity (HOMA). The XRD, DFT and MIR results show that the compound exists in the phenol-imine form in the solid state. HOMA indices support the aromatic structure of the compound. DFT calculations were performed to understand proton transfer process and relatively close values were obtained for the energies of tautomers. UV-vis studies prove the solvent dependence of the tautomerism in the compound by revealing the existence of both phenol-imine and keto-amine forms in polar solvents and only the phenol-imine form in apolar solvent. The TD-DFT results for the electronic transitions lead to the same conclusion as the absorption spectra. H-1 NMR and C-13 NMR studies at room and low (-60 degrees C) temperatures indicate that the tautomeric equilibrium occurs rapidly in the compound. Therefore, it is difficult to observe two tautomers. However, the presence of tautomeric structures is clearly seen in acetone d(6), alternatively underlying the solvent and temperature dependence of tautomerism in the title compound. (C) 2019 Elsevier B.V. All lights reserved.
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    Molecular and electronic structures of two new Schiff base compounds: (E)-2-bromo-6-[(2-bromo-4-methylphenylimino) methyl]-4-chlorophenol and (E)-2-bromo-6-[(4-bromo-3-methylphenylimino) methyl]-4-chlorophenol
    (Elsevier, 2021) Kirca, Basak Kosar; Kastas, Cigdem Albayrak; Ersanli, Cem Cuneyt
    Two new Schiff base compounds, (E)-2-bromo-6-[(2-bromo-4-methylphenylimino) methyl]-4-chlorophenol, (I) and (E)-2-bromo-6-[(4-bromo-3-methylphenylimino) methyl]-4-chlorophenol (II) have been synthesized and characterized by X-ray single crystal diffraction, FT-IR, UV-Vis and NMR spectroscopic techniques for this study. Moreover, the density functional theory calculations have been performed at the B3LYP method with 6-311G(d,p) basis set. The gas phase geometry optimizations of two possible forms resulting from the prototropic tautomerism of the title compounds have been obtained. While the X-ray and UV-Vis studies show that the compounds adopt OH tautomeric form in the solid state and solvent media, the density functional theory calculations also confirm that the OH tautomeric form is the most stable for both compounds. The crystal structures exhibit both inter-and intra-molecular hydrogen bond interactions, pi-pi stacking interactions and halogen bonds which play significant role in building the three dimensional network. (C) 2021 Elsevier B.V. All rights reserved.
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    Molecular Structure, FT-IR and UV-Vis Spectra, NBO, NPA and Fukui Function Analysis of (E)-2-((4-bromophenylimino)methyl)-3-methoxyphenol
    (Int Union Crystallography, 2016) Demircioglu, Zeynep; Buyukgungor, Orhan; Kastas, Cigdem Albayrak
    [No abstract available]
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    Scrutinizing the two new o-hydroxy Schiff bases from the point of tautomeric behavior and non-covalent interactions (H-bond, Br•••Br, π•••π and C-H•••π) in their supramolecular architectures
    (Elsevier, 2019) Kastas, Gokhan; Kastas, Cigdem Albayrak
    Two new Schiff bases, (E)-4,6-dibromo-2-[(5-chloro-2-methylphenylimino)methyl]-3-methoxyphenol (1) and (E)-4-bromo-2-[(4-bromophenylimino)methyl]-5-methoxyphenol (2), have been investigated by focusing on the prototropy-related-changes in the geometric parameters, the molecular planarity and the way of crystal packing. X-ray diffraction (XRD), density functional theory (DFT), Hartree-Fock theory (HF) and Moller-Plesset perturbation theory (MP2) and harmonic oscillator model of aromaticity (HOMA) studies show the preference of phenol-imine form by the compounds. The crystal packings of the compounds have been studied in detail by noting the importance of the substituent type and position in regulating the non-covalent interactions, thus, the formation of supramolecular networks. The results underline the fact that the halogen atoms of high polarizability and their presence in the appropriate position dominate the construction of supramolecular structure in Schiff bases. (C) 2019 Elsevier B.V. All rights reserved.
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    Spectroscopic, XRD, Hirshfeld surface and DFT approach (chemical activity, ECT, NBO, FFA, NLO, MEP, NPA& MPA) of (E)-4-bromo-2-[(4-bromophenylimino)methyl]-6-ethoxyphenol
    (Elsevier, 2019) Demircioglu, Zeynep; Kastas, Gokhan; Kastas, Cigdem Albayrak; Frank, Rene
    In the present work, the compound (E)-4-bromo-2-[(4-bromophenylimino)methyl]-6-ethoxyphenol was synthesized and characterized by spectroscopic (FT-IR and UV-Vis) and single crystal X-ray diffraction techniques. The intermolecular contacts in the compound was examined by Hirshfeld surfaces (HS) and fingerprint plots (FP) using the X-ray diffraction data. For other properties of interest, the geometry of the compound has been optimized by using the density functional theory (DFT) at B3LYP/6-311G (d,p) level. Molecular electrostatic potential (MEP), Fukui function (FF), nonlinear optical properties (NLO) and natural bond orbital (NBO) analyses have been performed and the global reactivity parameters have been obtained. The interactions between the title molecule and DNA bases (such as adenine, cytosine, guanine, and thymine) were investigated by using the ECT (electrophilicity-based charge transfer) method and Delta N (charge transfer). (C) 2019 Published by Elsevier B.V.
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    Structural, catalytic, antimicrobial and antioxidant properties of Cu(II)-complexes prepared by o-hydroxy Schiff bases with fluorine and ethoxy substituents
    (Taylor & Francis Ltd, 2025) Kastas, Gokhan; Kastas, Cigdem Albayrak; Avsar, Cumhur
    Cu(II) complexes of three Schiff bases were synthesized and characterized via X-ray diffraction, Fourier transform infrared, and UV-vis spectroscopies. The Schiff bases act as bidentate ligands, chelating Cu(II) ions in seesaw coordination geometry. Changing the substituent types and positions creates various non-covalent interactions within the crystal packings, yielding notable topological differences. GC-MS analysis reveals that Cu(II) complexes induce 1.38%-11.43% efficacy in Suzuki-Miyaura cross-coupling reactions. The biological activity of complexes correlates with substituent type and position in the aromatic ring. The one with ethoxy exhibits antimicrobial effects solely against Candida parapsilosis, while those with fluorine enhance the activity, particularly in the meta position.
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    Studies on the synthesis, spectroscopic analysis and DFT calculations on (E)-4,6-dichloro-2-[(2-chlorophenylimino)methyl]-3methoxyphenol as a novel Schiff's base
    (Elsevier, 2016) Yildirim, Arzu Ozek; Yildirim, M. Hakki; Kastas, Cigdem Albayrak
    In this study, we report synthesis, single crystal X-ray diffraction, FT-IR and Uv-Vis. characterizations and computational investigations of the (E)-4,6-dichloro-2-[(2-chlorophenylimino)methyl]-3methoxyphenol. The tautomeric equilibrium between enol, keto and transition state (TS) forms of (E)-4,6-dichloro-2-[(2-chlorophenylimino)methyl]-3-methoxyphenol have been investigated by considering the presence of the compound in vacuum and various solvents. Experimental studies clearly reveal that the title compound has enol form in solid state and ethanol solution. In addition, the enol, keto and TS structures of the compound have been investigated computationally. Intramolecular proton transfer process on the O-H center dot center dot center dot N hydrogen bond and transition state structure during the transfer process have been studied by scan calculations for vacuum and solvent media. Moreover, the stabilization energies of the title compound were computed by using second-order perturbation theory to have insight on the intra- and intermolecular interactions, interaction among bonds, conjugative interactions. To find out most reactive sites of the title molecule, condensed Fukui functions have been calculated by means of natural population analysis. Nonlinear optical property calculations of the compound indicate that the compound can be used as a NLO material. (C) 2016 Elsevier B.V. All rights reserved.
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    Synthesis, crystal structure and computational studies of a new Schiff base compound: (E)-4-bromo-2-ethoxy-6-{[(2-methoxyphenyl)-imino]methyl}phenol
    (Int Union Crystallography, 2018) Yildirim, Arzu Ozek; Gulsu, Murat; Kastas, Cigdem Albayrak
    The title compound, C16H16BrNO3, which shows enol-imine tautomerism, crystallizes in the monoclinic P2(1)/ c space group. All non-H atoms of the molecule are nearly coplanar, with a maximum deviation of 0.274 ( 3) angstrom. In the crystal, molecules are held together by weak C-H center dot center dot center dot O, pi-pi and C-H center dot center dot center dot pi interactions. The E/Z isomerism and enol/keto tautomerism energy barriers of the compound have been calculated by relaxed potential energy surface scan calculations with DFT methods. To observe the changes in the aromatic ring, HOMA aromaticity indexes were calculated during the scan process. Total energy and HOMA change curves were obtained to visualize results of the scan calculations.
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    Synthesis, crystal structure, computational chemistry studies and Hirshfeld surface analysis of two Schiff bases, (E)-2-[(4-bromo-2-methylphenylimino)methyl]-4-methylphenol and (E)-2-[(4-bromo-2-methylphenylimino)methyl]-6-methylphenol
    (Taylor & Francis Ltd, 2021) Demircioglu, Zeynep; Kastas, Cigdem Albayrak; Kastas, Gokhan; Ersanli, Cem Cuneyt
    In this study, two Schiff bases, (E)-2-[(4-bromo-2-methylphenylimino)methyl]-4-methylphenol (I) and (E)-2-[(4-bromo-2-methylphenylimino)methyl]-6-methylphenol (II) are synthesized and characterized by XRD and UV-Vis spectroscopy. The presence of various intermolecular interactions and 2 D-fingerprint regions are well supported by the Hirshfeld surface analysis. Also experimental optical energy band and gap studies are discussed. All theoretical computations (NBO, FMOs, MEP, NP, MP, FF) were calculated by Density Functional Theory (DFT) at B3LYP level by using 6-311 G(d,p) basis set. The interactions between the title molecules and DNA bases were investigated by using the ECT (electrophilicity-based charge transfer) method.
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    Synthesis, Spectroscopic, Conceptual DFT Characterization and Molecular Docking Studies of Two Versatile di-Bromobenzaldehyde Derived Compounds
    (Taylor & Francis Ltd, 2022) Yildirim, Arzu Ozek; Yildirim, Muhammet Hakki; Kastas, Cigdem Albayrak
    (E)-4,6-dibromo-2-[(2-chlorophenylimino)methyl]-3-methoxyphenol (I) and (E)-4,6-dibromo-2-[(2,5-difluorophenylimino)methyl]-3-methoxyphenol (II) Schiff base compounds were synthesized and characterized by using experimental XRD, FT-IR, UV-Vis. spectroscopic methods and computational methods. Geometry optimizations were done by using Gaussian type orbitals in Gaussian 09 W and Slater type orbitals in ADF2009 software. Spectroscopic studies show that the compounds prefer enol form in both solid and solvent. Scan calculations revealed that the reason for the enol form preference and the energy for prototropic tautomerism. From the biological activity estimations, it was determined that the compounds could be a Monoamine Oxidase Type B inhibitor, and comparative in-silico molecular docking studies with reverse docking of human monoamine oxidase type B protein were performed. Theoretical NLO calculations show that the second-order polarizability values of I and II were over 18 and 13 times that of the urea. Conceptual DFT studies were carried out to determine the reactivity descriptors of the molecules.
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    Synthesis, structural characterization and computational studies of (E)-4-bromo-2((3-chlorophenylimino)methyl)-6-ethoxyphenol
    (Elsevier, 2016) Yildirim, Arzu Ozek; Kastas, Cigdem Albayrak; Gulsu, Murat
    The present work reports on synthesis, single crystal X-ray diffraction, FT-IR, Uv-Vis., H-1 and C-13 NMR and theoretical calculations of the (E)-4-bromo-2-((3-chlorophenylimino)methyl)-6-ethoxyphenol compound. This study mainly focused on prototropic tautomerism and intramolecular proton transfer of (E)-4-bromo-2-((3-chlorophenylimino)methyl)-6-ethoxyphenol in solvent media and in solid state. Xray and FT-IR studies clearly reveals that the title compound exist in the enol form in solid state. Due to the dependence of prototropic tautomerism on solvent types, UV-Vis. spectra of the title compound were recorded in benzene, in chloroform and in ethanol. With the aid of theoretical calculations, important bands in the electronic spectrum were defined by means of frontier molecular orbitals. Intramolecular proton transfer process on the O-H center dot center dot center dot N hydrogen bond and transition state structure during the transfer process were investigated by scan calculations in the vacuum and in the different solvents. H-1 and C-13 NMR spectra were recorded in CDCl3 and detailed interpretation have been made on the basis of the theoretical calculations. Also, the stabilization energies of the title compound were computed by using second-order perturbation theory in order to investigate the intra- and intermolecular interactions, interaction among bonds, conjugative interactions. Nonlinear optical property calculations of the compound indicate that the material can be used as a NLO material. (C) 2015 Elsevier B.V. All rights reserved.
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    The effect of the change in substituents' positions on the formation of supramolecular networks and the solvent type/substituent dependence of prototropic behavior in three new o-hydroxy Schiff bases
    (Elsevier, 2020) Kastas, Gokhan; Kastas, Cigdem Albayrak; Kirca, Basak Kosar; Ersanli, Cem Cuneyt
    The effect of substituent position on the formation of supramolecular topology, intra-molecular geometry and tautomeric behavior, and the dependence of prototropy on the solvent type have been investigated applying the XRD, UV-Vis, NMR, DFT, PES and HOMA methods on three new o-hydroxy Schiff bases. Based on key geometric parameters, total molecular energy and aromaticity calculations, the XRD, DFT and HOMA studies propose the phenol-imine structure as the most consistent tautomeric form for the compounds. PES and HOMA studies give results that relate the preference of the phenol-imine form to its high p-electron delocalization. For the solvent type dependence of tautomerism, the investigation of UV-Vis and NMR spectra and the PES studies for different solvent media reveals that the co-existence of two tautomeric structures becomes easier by increasing solvent polarity. As to the effect of substituent position on the supramolecular topology, XRD studies show that different substituent positions cause different types of non-covalent inter-molecular interactions in the crystal packings of the compounds. This is resulted in a significant change in the formation and topology of the supramolecular architecture, emphasizing the importance of a substituent position as a regulator in crystal engineering. (C) 2019 Elsevier B.V. All rights reserved.
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    The spectroscopic (FT-IR, UV-vis), Fukui function, NLO, NBO, NPA and tautomerism effect analysis of (E)-2-[(2-hydroxy-6-methoxybenzylidene)amino]benzonitrile
    (Pergamon-Elsevier Science Ltd, 2015) Demircioglu, Zeynep; Kastas, Cigdem Albayrak; Buyukgungor, Orhan
    A new o-hydroxy Schiff base, (E)-2-[(2-hydroxy-6-methoxybenzylidene)amino]benzonitrile was isolated and investigated by experimental and theoretical methodologies. The solid state molecular structure was determined by X-ray diffraction method. The vibrational spectral analysis was carried out by using FT-IR spectroscopy in the range of 4000-400 cm(-1). Theoretical calculations were performed by density functional theory (DFT) method using 6-31G(d,p) basis set. The results of the calculations were applied to simulated spectra of the title compound, which show excellent agreement with observed spectra. The UV-vis spectrum of the compound was recorded in the region 200-800 nm in several solvents and electronic properties such as excitation energies, and wavelengths were calculated by TD-DFT/B3LYP method. The most prominent transitions were corresponds to pi -> pi*. Hybrid density functional theory (DFT) was used to investigate the enol-imine and keto-amine tautomers of titled compound. The titled compound showed the preference of enol form, as supported by X-ray and spectroscopic analysis results. The geometric and molecular properties were compaired for both enol-imine and keto-amine forms. Additionally, geometry optimizations in solvent media were performed with the same level of theory by the integral equation formalism polarizable continuum (IEF-PCM). Stability of the molecule arises from hyperconjugative interactions, charge delocalization and intramolecular hydrogen bond has been analyzed using natural bond orbital (NBO) analysis. Mulliken population method and natural population analysis (NPA) have been studied. Also, condensed Fukui function and relative nucleophilicity indices calculated from charges obtained with orbital charge calculation methods (NPA). Molecular electrostatic potential (MEP) and non linear optical (NLO) properties are also examined. (C) 2014 Elsevier B.V. All rights reserved.
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    Theoretical analysis (NBO, NPA, Mulliken Population Method) and molecular orbital studies (hardness, chemical potential, electrophilicity and Fukui function analysis) of (E)-2-((4-hydroxy-2-methylphenylimino)methyl)-3-methoxyphenol
    (Elsevier Science Bv, 2015) Demircioglu, Zeynep; Kastas, Cigdem Albayrak; Buyukgungor, Orhan
    The molecular structure and spectroscopic properties of (E)-2-((4-hydroxy-2-methylphenylimino)-methyl)-3-methoxyphenol, were characterized by X-ray diffraction, FT-IR and UV-Vis spectroscopy. All of theoretical calculations and optimized geometric parameters have been calculated by using density functional theory (DFT) with hybrid method B3LYP by 6-31G(d,p) basis set. The title compound of C15H11N1O3 have been analyzed according to electronic and energetics behaviors for enol-imine and keto-amine tautomers. Both these tautomers engender six-membered ring due to intramolecular hydrogen bonded interactions. Two types of intramolecular hydrogen bonds (a) strong O-H center dot center dot center dot N interactions in enol-imine form and (b) N-H center dot center dot center dot O interactions in keto-amine form are compared particularly. The theoretical vibrational frequencies have been found in good agreement with the corresponding experimental data. A study on the electronic and optical properties, absorption wavelengths, excitation energy, dipole moment, molecular electrostatic potential (MEP) and frontier molecular orbital energies are performed using DFT method. Additionally, geometry optimizations in solvent media were performed with the same level of theory by the polarizable continuum model (PCM). The effect of solvents on the tautomeric stability has been investigated. Mulliken Population Method and natural population analysis (NPA) have been studied. NBO analysis is carried out to picture the charge transfer between the localized bonds and lone pairs. The local reactivity of the molecule has been studied using the Fukui function. NLO properties related to polarizability and hyperpolarizability are also discussed. (C) 2015 Elsevier B.V. All rights reserved.
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    X-ray structural, spectroscopic and computational approach (NBO, MEP, NLO, NPA, fukui function analyses) of (E)-2-((4-bromophenylimino)methyl)-3-methoxyphenol
    (Taylor & Francis Ltd, 2017) Demircioglu, Zeynep; Kastas, Cigdem Albayrak; Buyukgungor, Orhan
    The title compound was isolated and investigated by experimental Xray diffraction method and density functional theory (DFT) calculational properties and spectroscopic methodologies. The experimental investigations of the compound indicated the molecule seems to be in enol form. DFT calculations are performed both for enol and keto tautomers of the title compound. Additionally chemical activity, electronic transmission and property effect on different solvents, molecular electrostatic potential (MEP), non-linear OPtical ProPetties Mulliken PoPulation method, natural population analysis (NPA), natural bond orbital (NBO) and Fukui function analyses have been studied.