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Balachandran V.,Aa Government Arts College | Nataraj A.,Thanthai Hans Roever College | Karthick T.,Vivekanandha College for Women
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2013

FT-Raman and FT-IR spectra for 2-hydroxy-p-toluic acid molecule had been recorded in the regions 3500-100 cm-1 and 4000-400 cm-1, respectively. Vibrational frequencies have been calculated in optimum state by employing density functional theory (DFT) and Hartree Fock (HF) methods with 6-311++G(d,p) basis set in monomeric form. SQM force fields have also been used to calculate potential energy distributions in order to make conspicuous vibrational assignments. Optimized geometries of the molecule had been interpreted and compared. The electric dipole moment and first hyperpolarizability values of the investigated molecule were computed using ab initio and DFT calculations. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond analysis. The results show that charge in electron density (ED) in the σ* antibonding orbitals and E(2) energies confirms the occurrence of ICT within the molecule. © 2012 Elsevier B.V. All rights reserved. Source


Nataraj A.,Thanthai Hans Roever College | Balachandran V.,Aa Government Arts College | Karthick T.,Vivekanandha College for Women | Karabacak M.,Afyon Kocatepe University | Atac A.,Celal Bayar University
Journal of Molecular Structure | Year: 2012

The FT-IR and FT-Raman spectra of 3,5-pyridinedicarboxylic acid (dinicotinic acid, C 7H 5NO 4) in the solid phase were recorded. The fundamental vibrational wavenumbers, intensities of vibrational bands and the optimized geometrical parameters of the compound are evaluated using HF and DFT (B3LYP) methods with 6-311G(d) basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The computed dimer parameters also show agreement with experimental data. The complete assignments were performed on the basis of the total energy distribution (TED). Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. UV-visible spectrum of the compound was recorded in the region 200-400 nm and the electronic properties HOMO and LUMO energies were measured by time-dependent TD-DFT approach. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures were calculated. © 2012 Elsevier B.V. All rights reserved. Source


Nataraj A.,Thanthai Hans Roever College | Balachandran V.,Aa Government Arts College | Karthick T.,Vivekanandha College for Women
Journal of Molecular Structure | Year: 2013

In this work, the vibrational spectral analysis was carried out using Raman and infrared spectroscopy in the range 4000-400 cm-1 and 3500-100 cm-1, respectively, for the 2-hydroxy-5-bromobenzaldehyde (HBB). The experimental spectra were recorded in the solid phase. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) with the standard B3LYP/6-311G++(d,p) method and basis set. Normal co-ordinate calculations were performed with the DFT force field corrected by a recommended set of scaling factors yielding fairly good agreement between observed and calculated frequencies. Simulation of infrared and Raman spectra utilizing the results of these calculations led to excellent overall agreement with the observed spectral patterns. The complete assignments were performed on the basis of the potential energy distribution (PED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The optimized geometric parameters (bond lengths and bond angles) were compared with experimental values of related compound. The stability of the molecule arising from hyper conjugative interactions and the charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The directly calculated ionization potential (IP), electron affinity (EA), electronegativity (χ), electrophilicity index (ω), hardness (η), chemical potential (μ), and first electron excitation (τ) are all correlated with the HOMO and LUMO energies with their molecular properties. These show that charge transfer occurs within the molecule. Furthermore, molecular electrostatic potential maps (MESP) of the molecule have been calculated. © 2012 Elsevier B.V. All rights reserved. Source


Balachandran V.,Aa Government Arts College | Karthick T.,Vivekanandha College for Women | Perumal S.,St Hindu College | Nataraj A.,Thanthai Hans Roever College
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2012

The potential energy surface scan for the selected dihedral angle of 6-nitro-m-toluic acid (NTA) has been performed to identify stable conformer. The optimized structure parameters and vibrational wavenumbers of stable conformer have been predicted by density functional B3LYP method with 6-311++G(d,p) basis set. The formation of dimer species through carboxylic acid group of the title molecule has also been discussed. The theoretical dimer geometries have been compared with that of monomer and the variations of bond lengths and bond angles upon dimerization were also discussed. Natural bond orbital (NBO) analysis has been performed on both monomer and dimer geometries. The significant changes in occupancies and the energies of bonding and anti-bonding orbitals upon dimerization have been explained in detail. The predicted frontier molecular orbital energies at B3LYP/6-311++G(d,p) method set show that charge transfer occurs within the molecule. The nucleophilic and electrophilic sites obtained from the molecular electrostatic potential (MEP) surface were compared with their derived fitting point charges. The vibrational wavenumbers of NTA affected profusely by the nitro group substitution in comparison to the toluic acid have been interpreted in this work. Copyright © 2012 Published by Elsevier B.V. All rights reserved. Source


Nataraj A.,Thanthai Hans Roever College | Balachandran V.,Aa Government Arts College | Karthick T.,Vivekanandha College for Women
Journal of Molecular Structure | Year: 2011

In this paper, we report a combined experimental and theoretical study on molecular structure; vibrational spectra of 4-hydroxy-3-methoxy-5- nitrobenzaldehyde (HMN) have been recorded using Fourier transform infrared spectroscopy (FT-IR) and FT-Raman measurements in the region of 4000-400 cm -1 and 3500-100 cm-1, respectively. The molecular geometry, harmonic vibrational frequencies, bonding features, total energy, Mulliken atomic charges and thermodynamic properties for most stable conformer of HMN in ground state were obtained by density functional theory (DFT) with the standard B3LYP/6-311++G(d,p) basis set combinations, and was scaled using various scale factors which yields a good agreement between observed and calculated frequencies. The vibrational spectra were interpreted with the aid of normal coordinate analysis based on scaled quantum mechanical force field. The results of the calculations were applied to simulated infrared and Raman spectra of the title compound, which showed good agreement with the observed spectra. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. © 2011 Elsevier B.V. All rights reserved. Source

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