Browsing by Author "Sinha, L"

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    Spectral investigation and theoretical study of zwitterionic and neutral forms of quinolinic acid
    Karabacak, M; Sinha, L; Prasad, O; Bilgili, S; Sachan, AK; Asiri, AM; Atac, A
    In this study, molecular structure and vibrational analysis of quinolinic acid (2,3-pyridinedicarboxylic acid), in zwitterionic and neutral forms, were presented using FT-IR, FT-Raman, NMR, UV experimental techniques and quantum chemical calculations FT-IR and FT-Raman spectra of 2,3-pyridinedicarboxylic acid (2,3-PDCA) in the solid phase were recorded in the region 4000-400 cm(-1) and 3500-0 cm(-1), respectively. The geometrical parameters and energies were obtained for zwitter and neutral forms by using density functional theory (DFT) at B3LYP/6-311++G(d,p) level of theory. 3D potential energy scan was performed by varying the selected dihedral angles using M06-2X and B3LYP functionals at 6-31G(d) level of theory and thus the most stable conformer of the title compound was determined. The most stable conformer was further optimized at higher level and vibrational wavenumbers were calculated. Theoretical vibrational assignment of 2,3-PDCA, using percentage potential energy distribution (PED) was done with MOLVIB program. C-13 and H-1 NMR spectra were recorded in DMSO. Chemical shifts were calculated at the same level of theory. The UV absorption spectra of the studied compound in ethanol and water were recorded in the range of 200-400 nm. The optimized geometric parameters were compared with experimental data. (C) 2015 Elsevier B.V. All rights reserved.
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    Experimental (FT-IR, FT-Raman, UV and NMR) and quantum chemical studies on molecular structure, spectroscopic analysis, NLO, NBO and reactivity descriptors of 3,5-Difluoroaniline
    Pathak, SK; Srivastava, R; Sachan, AK; Prasad, O; Sinha, L; Asiri, AM; Karabacak, M
    Comprehensive investigation of geometrical and electronic structure in ground as well as the first excited state of 3,5-Difluoroaniline (C6H5NF2) was carried out. The experimentally observed spectral data (FT-TR and FT-Raman) of the title compound was compared with the spectral data obtained by DFT/B3LYP method using 6-311++G(d,p) basis set. The molecular properties like dipole moment, polarizability, first static hyperpolarizability, molecular electrostatic potential surface (MEPs), and contour map were calculated to get a better insight of the properties of the title molecule. Natural bond orbital (NBO) analysis was applied to study stability of the molecule arising from charge delocalization. UV-Vis spectrum of the title compound was also recorded and the electronic properties, such as Frontier orbitals and band gap energies were measured by TD-DFT approach. Total and partial density of state (TDOS and PDOS) and also overlap population density of state (OPDOS) diagrams analysis were presented. Global and local reactivity descriptors were computed to predict reactivity and reactive sites on the molecule. H-1 and C-13 NMR spectra by using gauge including atomic orbital (GIAO) method of studied compound were compared with experimental data obtained. Moreover, the thermodynamic properties were evaluated. (C) 2014 Elsevier B.V. All rights reserved.
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    Quantum-chemical (DFT, MP2) and spectroscopic studies (FT-IR and UV) of monomeric and dimeric structures of 2(3H)-Benzothiazolone
    Sinha, L; Prasad, O; Karabacak, M; Mishra, HN; Narayan, V; Asiri, AM
    Molecular geometry and vibrational wavenumbers of 2(3H)-Benzothiazolone (C7H5NSO, HBT) was investigated using density functional (DFT/B3LYP) method with 6-311+G(d,p) basis set. The vibrational wavenumbers are found to be in good agreement with experimental FT-IR spectra. Hydrogen-bonded dimer of HBT, optimized by counterpoise correction, was studied by MP2 and DFT/B3LYP at the 6-311+G(d,p) level and the effects of molecular association through N-H-O hydrogen bonding were discussed. A detailed analysis of the nature of the hydrogen bonding, using topological parameters, such as electronic charge density, Laplacian, kinetic and potential energy density evaluated at bond critical points (BCP) has also been presented. The UV absorption spectra of the compound dissolved in ethanol and chloroform solutions were recorded in the range of 200-600 nm. The UV-vis spectrum of the title molecule was also calculated using TD-DFT method. The calculated energy and oscillator strength almost exactly reproduce the experimental data. Total and partial density of state (TDOS, PDOS) of the HBT in terms of HOMOs and LUMOs and molecular electrostatic potential (MEP) were calculated and analyzed. The electric dipole moment, polarizability and the first static hyper-polarizability values for HBT were calculated at the DFT/B3LYP with 6-311+G(d,p) basis set. The results also show that the HBT molecule may have nonlinear optical (NLO) comportment with non-zero values. Stability of the molecule arising from hyper-conjugative interactions and charge delocalization was analyzed using natural bond orbital (NBO) analysis. (C) 2013 Elsevier B.V. All rights reserved.
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    A combined experimental and theoretical investigation of 2-Thienylboronic acid: Conformational search, molecular structure, NBO, NLO and FT-IR, FT-Raman, NMR and UV spectral analysis
    Sachan, AK; Pathak, SK; Sinha, L; Prasad, O; Karabacak, M; Asiri, AM
    The solid state Fourier transform infrared (FT-IR) and Fourier transform Raman (FT-Raman) spectra of 2-Thienylboronic acid (2TBA), were recorded in the range of 4000-400 cm(-1) and 4000-100 cm(-1), respectively. DFT/B3LYP theory was used for the optimization of the ground state geometry and simulation of the infrared and Raman spectra of the title molecule. To determine lowest-energy molecular conformation of the studied molecule, the selected torsion angles were varied in steps of 10 degrees and complete 3D molecular energy profile was calculated. Among the four possible conformers (Trans-Trans, Cis-Cis, Trans-Cis and Cis-Trans), the most stable conformer of 2TBA is the Trans-Cis form. The vibrational wavenumbers and their assignments were carried out theoretically using the Gaussian09 set of quantum chemistry codes and the normal modes were calculated using MOLVIB program. Experimental FT-IR and FT-Raman spectra of the title compound were compared with the spectral data obtained by DFT/B3LYP method. Dipole moment, polarizability, first static hyperpolarizability and molecular electrostatic potential surface (MEPs) map have been calculated to get a better perception of the properties of the title molecule. Natural bond orbital (NBO) analysis was performed to study the stability of the molecule arising from charge delocalization. UV-Vis spectrum of the title molecule was also recorded (500-200 nm) in methanol and electronic properties such as frontier orbitals and energy gap were calculated by TD-DFT approach. The H-1 nuclear magnetic resonance (NMR) chemical shifts of the studied molecule were recorded in DMSO-d6 and calculated by Gauge-Including Atomic Orbital (GIAO) method. (C) 2014 Elsevier B.V. All rights reserved.
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    FT-IR, FT-Raman and UV spectroscopic investigation, electronic properties, electric moments, and NBO analysis of anethole using quantum chemical calculations
    Sinha, L; Prasad, O; Chand, S; Sachan, AK; Pathak, SK; Shukla, VK; Karabacak, M; Asiri, AM
    FT-IR and FT-Raman spectra of anethole (1-Methoxy-4-(1-propenyl)benzene), a flavoring agent of commercial value, have been recorded in the regions 4000-400 and 4000-100 cm(-1) respectively. The structure of the title molecule has been optimized and the structural parameters have been calculated by DFT/B3LYP method with 6-311++G(d,p) basis set. The fundamental vibrational wavenumbers as well as their intensities were calculated and a good agreement between observed and scaled calculated wavenumbers has been achieved. UV-Vis spectrum of the title compound was recorded in the region 200-500 nm and the electronic properties such as HOMO and LUMO energies and associated energy gap were calculated by Time dependent-density functional theory (TD-DFT) approach. Nonlinear optical (NLO) study divulges the nonlinear properties of the molecule. Stability of the title molecule arising from hyper-conjugative interactions and charge delocalization has been investigated using natural bond orbital (NBO) analysis. The theoretical results were found to be in coherence with the measured experimental data. (C) 2014 Elsevier B.V. All rights reserved.
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    Molecular structure, electronic properties, NLO, NBO analysis and spectroscopic characterization of Gabapentin with experimental (FT-IR and FT-Raman) techniques and quantum chemical calculations
    Sinha, L; Karabacak, M; Narayan, V; Cinar, M; Prasad, O
    Gabapentin (GP), structurally related to the neurotransmitter GABA (gamma-aminobutyric acid), mimics the activity of GABA and is also widely used in neurology for the treatment of peripheral neuropathic pain. It exists in zwitterionic form in solid state. The present communication deals with the quantum chemical calculations of energies, geometrical structure and vibrational wavenumbers of GP using density functional (DFT/B3LYP) method with 6-311++G(d,p) basis set. In view of the fact that amino acids exist as zwitterions as well as in the neutral form depending on the environment (solvent, pH, etc.), molecular properties of both the zwitterionic and neutral form of GP have been analyzed. The fundamental vibrational wavenumbers as well as their intensities were calculated and compared with experimental FT-IR and FT-Raman spectra. The fundamental assignments were done on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanical (SQM) method. The electric dipole moment, polarizability and the first hyperpolarizability values of the GP have been calculated at the same level of theory and basis set. The nonlinear optical (NLO) behavior of zwitterionic and neutral form has been compared. Stability of the molecule arising from hyper-conjugative interactions and charge delocalization has been analyzed using natural bond orbital analysis. Ultraviolet visible (UV-Vis) spectrum of the title molecule has also been calculated using TD-DFT method. The thermodynamic properties of both the zwitterionic and neutral form of GP at different temperatures have been calculated. (C) 2013 Elsevier B.V. All rights reserved.
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    A combined experimental and theoretical DFT (B3LYP, CAM-B3LYP and M06-2X) study on electronic structure, hydrogen bonding, solvent effects and spectral features of methyl 1H-indol-5-carboxylate
    Srivastava, R; Al-Omary, FAM; El-Emam, AA; Pathak, SK; Karabacak, M; Narayan, V; Chand, S; Prasad, O; Sinha, L
    Investigation of ground state geometry, molecular properties and electronic structure of methyl 1H-indol-5-carboxylate has been reported for the first time using the implements of density functional theory. The two possible conformers of the title compound were first optimized at B3LYP/6-31G(d) and then further at B3LYP, M06-2X and CAM-B3LYP functionals at 6-311++G(d,p) basis set. A comprehensive vibrational analysis has been performed for both the conformers at B3LYP/6-311++G(d,p). Good agreement between theoretical spectral data with experimental spectra has been obtained. Polarizability and first static hyperpolarizability have been compared at different functionals used in the present study. To estimate the intra-molecular delocalization along with the inter-molecular interaction, the NBO analysis has been done for monomer and dimer of the title molecule. Topological parameters at the bond critical point involved in intermolecular hydrogen-bonding have also been calculated using AIM theory to assess the strength of hydrogen bonding. Effects of solvents (water, carbon tetrachloride and chloroform) on the optimized geometry and the inter-molecular hydrogen bonding have been evaluated. UV-Vis spectrum of the title compound was also recorded and electronic properties such as frontier orbitals and their corresponding energy gap have also been calculated by TD-DFT approach.
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    FT-IR, FT-Raman, NMR, UV and quantum chemical studies on monomeric and dimeric conformations of 3,5-dimethyl-4-methoxybenzoic acid
    Karabacak, M; Sinha, L; Prasad, O; Asiri, AM; Cinar, M; Shukla, VK
    Extensive spectroscopic investigations along with theoretical quantum chemical studies on 3,5-dimethyl-4-methoxybenzoic acid (DMMBA) have been consummated. The fundamental vibrational transitions were addressed by experimental FT-IR (4000-400 cm(-1)) and FT-Raman (4000-10 cm(-1)) techniques and density functional calculations at B3LYP/6-311++G(d,p) and B3LYP/6-311++G(df,pd) levels of theory. The H-1, C-13 and DEPT 135 NMR spectra of studied compound were recorded in deuterated dimethylsulfoxide (DMSO-d6), and compared with computed data obtained by using gauge including atomic orbital (GIAO) method. The electronic absorption spectra in methanol and ethanol solution were evaluated in the range of 200-400 nm, and TD-DFT method was chosen for computational study. The spectroscopic and theoretical results were compared to the corresponding properties for monomer and dimer structures for the most stable conformer. Stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Moreover, the thermodynamic and nonlinear optical (NLO) properties were evaluated. (C) 2013 Elsevier B.V. All rights reserved.
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    Conformational and spectroscopic behaviors of 2,4-xylyl isothiocyanate
    Cinar, M; Karabacak, M; Chand, S; Shukla, VK; Sinha, L; Prasad, O; Singh, MP; Asiri, AM
    This study aims to identify the conformational and spectroscopic characteristics of 2,4-xylyl isothiocyanate (C9H9NS) compound via experimental and computational methods. To accomplish this, density functional theory (DFT), with the B3LYP functional was used to determine ground state conformation, vibrational wavenumbers and also isotropic chemical shifts of the title molecule. Experimentally, vibrational features of the compound were evaluated by FT-IR and FT-Raman spectroscopic analysis in the solid phase. On the basis of these studies, the conformational and spectroscopic behaviors of 2,4-xylyl isothiocyanate were interpreted. The fundamental vibrational wavenumbers as well as their intensities were computed, and a good correlation between experimental and scaled calculated wavenumbers was observed. The polarizability, first hyperpolarizability and dipole moment values of 2,4-xylyl isothiocyanate were calculated at the same level of theory and basis set. The results show that 2,4-xylylisothiocyanate molecule possesses nonlinear optical (NLO) behavior with non-zero values. Stability of the molecule arising from hyper-conjugative interactions and charge delocalization was analyzed using natural bond orbital (NBO) analysis. (c) 2015 Elsevier B.V. All rights reserved.
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    An experimental and theoretical investigation of Acenaphthene-5-boronic acid: Conformational study, NBO and NLO analysis, molecular structure and FT-IR, FT-Raman, NMR and UV spectra
    Karabacak, M; Sinha, L; Prasad, O; Asiri, AM; Cinar, M
    The solid state Fourier transform infrared (FT-IR) and FT-Raman spectra of Acenaphthene-5-boronic acid (AN-5-BA), have been recorded in the range 4000-400 cm(-1) and 4000-10 cm(-1), respectively. Density functional theory (OFT), with the B3LYP functional was used for the optimization of the ground state geometry and simulation of the infrared and Raman spectra of the molecule. The vibrational wave numbers and their assignments were examined theoretically using the Gaussian 09 set of quantum chemistry codes and the normal modes were assigned by a scaled quantum mechanical (SQM) force field approach. Hydrogen-bonded dimer of AN-5-BA, optimized by counterpoise correction, has also been studied by B3LYP at the 6-311++G(d,p) level and the effects of molecular association through O-H center dot center dot center dot O hydrogen bonding have been discussed. The H-1 and C-13 nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by Gauge-Including Atomic Orbital (GIAO) method. Natural bond orbital (NBO) analysis has been applied to study stability of the molecule arising from charge delocalization. UV spectrum of the title compound was also recorded and the electronic properties, such as frontier orbitals, and band gap energies were measured by TD-DFT approach. The first order hyperpolarizability beta , its components and associated properties such as average polarizability and anisotropy of the polarizability (alpha and Delta alpha) of AN-5-BA was calculated using the finite-field approach. (C) 2013 Elsevier B.V. All rights reserved.
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    Spectral features, electric properties, NBO analysis and reactivity descriptors of 2-(2-Benzothiazolylthio)-Ethanol: Combined experimental and DFT studies
    Srivastava, R; Sinha, L; Karabacak, M; Prasad, O; Pathak, SK; Asiri, AM; Cinar, M
    Quantum chemical calculations of ground state energy, geometrical structure and vibrational wavenumbers, nuclear magnetic behaviors, electronic absorption spectra along with the nonlinear optical properties of 2-(2-benzothiazolylthio)-ethanol (BTZTE) were carried out using density functional (DFT/B3LYP) method with 6-311++G(d,p) as basis set. The FT-IR and FT-Raman spectra were measured in the condensed state. The fundamental vibrational wavenumbers as well as their intensities were calculated, and a good correlation between experimental and scaled calculated wavenumbers was accomplished. The electric dipole moment, polarizability and the first hyperpolarizability values of the BTZTE were calculated at the same level of theory and basis set. The results show that the BTZTE molecule possesses nonlinear optical (NLO) behavior with non-zero values. Stability of the molecule arising from hyper-conjugative interactions and charge delocalization was analyzed using natural bond orbital (NBO) analysis. UV spectrum of the studied molecule was recorded in the region 200-500 nm and the electronic properties were predicted by time-dependent DFT approach. The calculated transition energies are in good concurrency with the experimental data. H-1 nuclear magnetic resonance (NMR) chemical shifts of the title molecule were calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. The thermodynamic properties of the studied compound at different temperatures were calculated. Global and local reactivity descriptors were computed to predict reactivity and reactive sites on the molecule. (C) 2014 Elsevier B.V. All rights reserved.