R. John Xavier

FT Raman and FT–IR spectral studies of 3-mercapto-1,2,4-triazole

The FT-IR and FT Raman spectra of 3-mercapto-1,2,4-triazole have been recorded. The observed frequencies were assigned to various modes of vibrations on the basis of normal coordinate calculations, assuming Cs point group symmetry. The potential energy distribution associated with normal modes is also reported here. The assignment of fundamental vibrations agrees well with the calculated frequencies.

FTIR, FT-Raman, scaled quantum chemical studies of the structure and vibrational spectra of 1,5-dinitronaphthalene.

The solid phase FTIR and FT-Raman spectra of 1,5-dinitronaphthalene (DNN) have been recorded in the regions 4000-50 and 3500-100cm(-1), respectively. The spectra were interpreted with the aid of normal coordinate analysis following full structure optimization and force field calculation based on density functional theory using standard B3LYP/6-31G* and B3LYP/6-311+G** methods and basis set combinations and was scaled using various scale factors yielding fairly good agreement between observed and calculated frequencies. Based on the present good quality scaled quantum mechanical force field, a reliable description of the fundamentals was provided and the assignments have been proposed with the help of normal coordinate analysis. The infrared and Raman spectra were also predicted from the calculated intensities. Comparison of the simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.

Density functional theory study on characterization of 3-chloro-1,2-benzisothiazole.

The FT-IR and FT-Raman spectra of 3-chloro-1,2-benzisothiazole (CBT) have been recorded and analyzed. Theoretical information on the optimized geometry, harmonic vibrational frequencies, infrared and Raman intensities were obtained by means of density functional theory (DFT) gradient calculations, using 6-311++G(d,p) basis set. Mulliken population analysis shows charge distribution on the molecule. Thermodynamic properties like entropy, heat capacity, zero point energy have been calculated for the molecule. The calculated HOMO and LUMO energies show the charge transfer occurs within the molecule. Stability of the molecule has been analyzed using Natural Bond Orbital (NBO) and Natural Localized Molecular Orbital (NLMO) analysis. The results of the calculations were applied to simulated spectra of the title compound, which show the excellent agreement with the observed spectra.

FT-IR, FT-Raman, ab initio and DFT studies, HOMO–LUMO and NBO analysis of 3-amino-5-mercapto-1,2,4-triazole

The molecular vibrations of 3-amino-5-mercapto-1,2,4-triazole (AMT) have been investigated in polycrystalline sample, at room temperature, by Fourier transform infrared (FT-IR) and FT-Raman spectroscopies. A detailed vibrational spectral analysis has been carried out and assignments of the fundamental modes have been proposed on the basis of peak positions and relative frequencies, atomic charges, HOMO-LUMO energies and several thermodynamic properties in the ground state were calculated using ab initio Hartree-Fock (HF) and Density Functional Theory, (B3LYP) with 6-311G(d,p) and 6-311++G(d,p) basis sets. With the aid of scaling procedures, observed wave numbers in FT-IR and FT-Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wave numbers in the expected range. The theoretical IR and Raman spectra have also been constructed. Natural Bond Orbital (NBO) study explains charge delocalization of the molecule.

Spectroscopic (FTIR, FT-Raman, 13C and 1H NMR) investigation, molecular electrostatic potential, polarizability and first-order hyperpolarizability, FMO and NBO analysis of 1-methyl-2-imidazolethiol.

In this work, experimental and theoretical study on the molecular structure and vibrational spectra of 1-methyl-2-imidazolethiol (MIME) were presented. The vibrational frequencies of the title compound were obtained theoretically by ab initio HF and DFT (B3LYP/LSDA) employing 6-311G (d,p) and 6-311++G(d,p) basis sets and compared with experimental spectral bands (FTIR and FT-Raman). The thermodynamic properties of the studied compound have been computed at different temperatures. The atomic charges and charge delocalization of the molecule have been analyzed by natural bond orbital (NBO) analysis. The reactivity sites are identified by mapping the molecular electrostatic potential (MESP) surface. Electronic properties HOMO and LUMO energies were measured by time-dependent TD-DFT approach. Besides, (13)C and (1)H nuclear magnetic resonance (NMR) chemical shifts of the molecule in chloroform solvent calculated using the Gauge-Independent Atomic Orbital (GIAO) method are found to be in good agreement with experimental values.

Experimental and theoretical spectroscopic studies, HOMO-LUMO, NBO and NLMO analysis of 3,5-dibromo-2,6-dimethoxy pyridine.

The molecular vibrations of 3,5-dibromo-2,6-dimethoxy pyridine (DBDMP) have been investigated in polycrystalline sample, at room temperature, by Fourier transform infrared (FT-IR) and FT-Raman spectroscopies. The vibrational frequencies of the fundamental modes of the compound have been precisely assigned and theoretical results were compared with the experimental vibrations. Theoretical information on the optimized geometry, harmonic vibrational frequencies, infrared and Raman activities were obtained by means of ab initio and density functional theory (DFT) gradient calculations, using 6-311++G(d,p) basis set. Thermodynamic properties like entropy, heat capacity and zero point energy have been calculated for the molecule. HOMO-LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using Natural Bond Orbital (NBO) and Natural Localized Molecular Orbital (NLMO) analysis. The Molecular Electrostatic Potential (MEP) analysis reveals the sites for electrophilic attack and nucleophilic reactions in the molecule.

Conformational stability, vibrational spectra, HOMO-LUMO and NBO analysis of 1,3,4-thiadiazolidine-2,5-dithione with experimental (FT-IR and FT-Raman) techniques and scaled quantum mechanical calculations.

The experimental and theoretical study on the structure and vibrations of 1,3,4-thiadiazolidine-2,5-dithione (TDZD) is presented. The FT-IR spectra (4000-400 cm(-1)) and the FT-Raman spectra (4000-50 cm(-1)) of the title molecule have been recorded. The energies of TDZD were obtained for all the possible four conformers from HF and DFT with 6-311G(d,p) and 6-311++G(d,p) basis set calculations. From the computational results, conformer C4 is identified as the most stable conformers of TDZD. The spectroscopic and theoretical results are compared with the corresponding properties for TDZD of C4 conformer. The temperature dependence of thermodynamic properties has been analyzed. Molecular stability and bond strength were investigated by applying the natural bond orbital analysis (NBO). The calculated HOMO and LUMO energies show that charge transfer occurs in the molecules. Information about the size, shape, charge density distribution, and site of chemical reactivity of the molecules has been obtained by mapping electron density isosurface with electrostatic potential (ESP). The dipole moment (λ) and polarizability (α), anisotropy polarizability (Δα) and first hyperpolarizability (βtotal) of the molecule have been reported.

Quantum chemical calculations, vibrational studies, HOMO–LUMO and NBO/NLMO analysis of 2-bromo-5-nitrothiazole

The complete vibrational assignment and analysis of the fundamental modes of 2-bromo-5-nitrothiazole (BNT) was carried out using the experimental FTIR and FT-Raman data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically for the optimized geometry of the compound from the ab initio HF and DFT-B3LYP gradient calculations employing 6-311++G(d,p) basis set. Thermodynamic properties like entropy, heat capacity and zero point energy have been calculated for the molecule. HOMO-LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using Natural Bond Orbital (NBO) and Natural Localized Molecular Orbital (NLMO) analysis. Important non-linear properties such as electric dipole moment and first hyperpolarizability of BNT have been computed using B3LYP quantum chemical calculation.

Spectroscopic investigations, quantum chemical calculations, HOMO–LUMO and NBO/NLMO analysis of 4-pyridinecarbohydrazide

The FT-IR and FT-Raman spectra of 4-pyridinecarbohydrazide have been recorded. The complete vibrational assignment and analysis of the fundamental modes was carried out using the experimental data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically for the optimized geometry of the compound from the DFT-B3LYP gradient calculations employing 6-311++G(d,p) basis set. The (1)H and (13)C NMR chemical shifts have been simulated. Thermodynamic properties have been calculated at different temperatures. HOMO-LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using Natural Bond Orbital (NBO) and Natural Localized Molecular Orbital (NLMO) analysis.

Ab initio, density functional computations, FT-IR, FT-Raman and molecular geometry of 4-morpholine carbonitrile

The 4-morpholine carbonitrile (4MC) was investigated by vibrational spectroscopy and quantum chemical methods. The solid phase FT-IR and FT-Raman spectra were recorded in the region 4000-400 cm(-1) and 3500-50 cm(-1), respectively. The molecular geometry and vibrational frequencies of 4MC have been calculated in the ground state by using the ab initio Hartree-Fock and density functional method (B3LYP) with 6-311++G(d, p) basis set. The observed and calculated frequencies are found to be in good agreement. The calculated HOMO and LUMO energies show the charge transfer occurs within the molecule. Stability of the molecule arising from hyper conjugative interactions and charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The theoretical FT-IR and FT-Raman spectra for the title compound have also been constructed.