Vibrational Analysis First Hyperpolarizability and Homo-Lumo Analyses of 2, 4, 6-Trimethyl Benzaldehyde
In the present study, the FT-IR and FT-Raman spectra of 2,4,6-Trimethylbenzaldehyde have been recorded in the region 4000–400 cm_1 and 3500–50 cm_1, respectively. The fundamental modes of vibrational frequencies of (TMB) are assigned. Theoretical information on the optimized geometry, harmonic vibrational frequencies, infrared and Raman intensities were obtained by means of ab initio Hartree–Fock (HF) and density functional theory (DFT) gradient calculations with complete relaxation in the potential energy surface using 6-31+G(d,p)) basis set. The vibrational frequencies which were determined experimentally from the spectral data are compared with those obtained theoretically from ab initio and DFT calculations. A close agreement was achieved between the observed and calculated frequencies by refinement of the scale factors. The infrared and Raman spectra were also predicted from the calculated intensities. Thermodynamic properties like entropy, heat capacity, zero point energy, have been calculated for the molecule. The calculated HOMO–LUMO energy gap reveals that charge transfer occurs within the molecule. Unambiguous vibrational assignment of all the fundamentals was made using the total energy distribution (TED).
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Molecular structure and vibrational assignments of L-tyrosine: a detailed experimental and density functional theoretical study
L–tyrosine (C9H11NO3) is one of the 20 naturally occurring amino acids. L- tyrosine has been crystallized in silica gel by double diffusion technique which had rosette like shape. Crystal structure and spectral properties are analyzed using powder X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and UV-Vis transmittance studies. Optical band gap energy of L –tyrosine crystallite is estimated as 4.28 eV. In this study, the structural properties of L-tyrosine (C9 H11 NO3) have been studied using density functional theory (DFT) employing B3LYP exchange correlation. The geometry of the molecule was fully optimized at B3LYP/ 6-311G (d,p) level of theory. The optimized geometrical parameters obtained by DFT calculations are in good conformity with single crystal XRD data. The vibrational frequencies were calculated and fundamental vibrations were assigned based on the scaled theoretical wavenumbers. 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by using the gauge-invariant atomic orbital (GIAO) method. A study on the electronic properties, such as HOMO and LUMO energies were performed by using DFT approach. Finally, geometric parameters, vibrational frequencies, chemical shifts and absorption wavelengths were compared with available experimental data of the molecule. Quantum chemical parameters such as the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital energy (LUMO), energy gap (E), dipole moment (µ), electro negativity (?), chemical potential (Pi), global hardness (?), softness (?) and natural atomic charges were calculated. A good correlation was found between the theoretical data and the experimental results. The thermodynamic properties of the studied compound at room temperatures were calculated.
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Density Functional Theory studies on the structure and vibrational assignments of N, N-Dimethylaniline
The FT-IR and FT-Raman spectra of the N, N-Dimethylaniline (NNDMA) was recorded in the range 4000–400 cm–1 and 3500–100 cm–1, respectively. Theoretical information on the optimized geometry, harmonic vibrational frequencies, Infrared and Raman intensities were obtained by means of density functional theory (DFT) using standard B3LYP/6-311++G** level. This information was used in the assignment of the various fundamentals. Comparison of the simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.
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Hydrogen Adsorption on Sodium-attached Graphene
First principles calculations based on Density Functional Theory were carried out to study hydrogen storage capacity of sodium doped graphene. The pure graphene exhibits low hydrogen storage capacity hence we modified graphene by doping of sodium. Sodium occupies the empty (hollow) position on graphene with average carbon sodium bond-length of 2.64 Å. This investigation predicts that positively charged sodium atom on graphene physisorbed maximum six hydrogen molecules with the average adsorption energy 0.20 eV/H2 amounting gravimetric density of 9.2 wt%. Mulliken population analysis shows that the charge transfer from sodium to graphene is responsible for higher hydrogen uptake than the pure graphene sheet.
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Mixed ligand complexes of Ru(II) complexes with 5,6-dimethyl -3-pyridin-2-yl-[1,2,4]triazine: Synthesis, Characterization and Quantum Chemical Study using Semi-empirical PM 3 and Ab initio Methods
The condensation product between 2,6-diacetylpyridinedihydrazone and pyridine-2-aldehyde were prepared and this was reacted with cis-Ru(phen)2Cl2.2H2O and cis-Ru(bipy)2Cl2.2H2O to form two mixed – ligand complexes. The complexes were characterized using elemental analyses, infrared and electronic spectra, mass spectra, 1H NMR, and the molar conductances determined. The elemental analyses data is satisfactory with the formation of the prepared complexes which conformed to the electrocyclisation of the introduced ligand. The mass spectra data is consistent with the molecular structural patterns of the complexes. The conductivity measurement revealed that the complexes were 1:2 electrolytes. Quantum chemical methods are used to calculate the binding and stabilization energies of the two complexes which suggested that binding and stabilization energies of [Ru(phen)2L]2+ are thermodynamically more favourable compared to [Ru(bipy)2L]2+ .
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Physicochemical Properties of Epoxy Polyol with Isophorne Diisocyanate based two Component Polyurethane Coatings
Polyurethane coatings are formed from the chemical reaction between polyol and polyisocyanate hardener. By varying the concentration of isophorne diisocyanate, two component polyurethane coatings have been prepared with the blending of epoxy polyol and isophorne diisocyanate (IPDI). Totally seven types of experiments were conducted with the prepared blend mixtures. All these experiments were based on the solid contents of the hydroxyl equivalent weights of epoxy polyol and NCO equivalent weight of IPDI. Films were coated on the mild steel using the clear polyurethane solution. The Electrochemical Impedance Spectroscopy (EIS) was used to characterize the coated film. The formation of the polyurethane was confirmed FTIR spectral data.
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Theoretical Study of Tautomerism of N-(Pyridine-2yl)Acetamide by Density Functional Theory(DFT)
The geometries of various rotamers, tautomers and isomers of N-(pyridine -2yl)acetamide have been studied using the density functional theory (DFT) method at the level of B3LYP employing 6-311++G(d,p) basis set. We report the enthalpies, Gibbs free energy, entropy, relative stability and tautomeric equilibrium constants for the title compound isomers at 298.15 K in gas phase. The most stable A4 is taken as reference to obtain the relative energetic stability of other rotamers. Calculated values for the equilibrium between these some tautomers show that pKT value is negative values. If the pKT was positive, equilibrium moved from right towards the lift and when it was negative, equilibrium moved from left towards the right.
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Vibrational spectral investigations, Nlo and homo lumo analysis of 4-chloro-2,6-dibromoaniline
The solid phase FTIR and FT-Raman spectra of 4-chloro-2, 6-dibromoaniline (CDBA) have been recorded in the region 4000-400 cm-1 and 3500-100 cm-1, respectively. The spectra were interpreted with the aid of normal coordinate analysis following a full structure optimization and force field calculation based on the density functional theory (DFT) using the standard HF/6-31+G(d,p) and B3LYP/6-31+G(d,p) methods and basis set combination. A close agreement between the observed and calculated frequencies by refinement of the scale factor. The values of electric dipole moment (? and First-order hyperpolarizability(?) of the compound were computed using ab-initio quantum mechanical calculations.The calculation results also show that the PFA molecule might have microscopic nonlinear optical (NLO) behavior with non-zero values. HOMO and LUMO energy gap explains the eventual charge transfer interaction taking place within the molecule.
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Theoretical studies of the Vibrational spectra and Molecular electrostatic potentials (MEP) of Allopurinol isomers
The harmonic wave numbers of allopurinol were calculated by using of density functional theory with B3LYP/6-311++ G(d,p) level. The molecular electrostatic potentials (MEP) of allopurinol isomers were calculated with help of Spartan 10 software at the B3LYP/6-31++ (d,p) level , and the molecular surface was taken to be the 0.002 au contour of the electron density. These MEP map surfaces show that different colors, the red color shows positive potentials and blue color shows negative potentials. From the MEP results, the positive potentials sites are located an electronegative nitrogen and oxygen atoms and the negative potentials sites are located around the hydrogen atoms in the isomers. These potentials sites are mainly give the information about intermolecular interactions possible in the molecule.
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Geometry and vibrational analysis of 2-amino thiazole - quantum chemical study
The Fourier transform infrared (FT-IR) and FT-Raman of 2-Amino thiazole (2-AT) have been recorded and analyzed. The equilibrium geometry, bonding features and harmonic vibrational frequencies have been investigated with the help of ab initio and density functional theory (DFT) methods. The assignments of the vibrational spectra have been carried out. The optimized geometric bond lengths and bond angles obtained by computation show good agreement with experimental data of the relative compound. The computed parameters also show good agreement with experimental data. The calculated HOMO and LUMO energies also show that charge transfer occurs within the molecule. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. The results show that charge in electron density (ED) in the ?* and ?* antibonding orbital and second order delocalization energies E(2) confirms the occurrence of intramolecular charge transfer (ICT) within the molecule. Finally the calculations results were applied to simulated infrared and Raman spectra of the title compound which show good agreement with observed spectra.
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