R Santhanam

Publications (5)10.49 Total impact

• Article: Primidone - An antiepileptic drug - characterisation by quantum chemical and spectroscopic (FTIR, FT-Raman, (1)H, (13)C NMR and UV-Visible) investigations.

  V Arjunan, R Santhanam, S Subramanian, S Mohan
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  ABSTRACT: The solid phase FTIR and FT-Raman spectra of primidone were recorded in the regions 4000-400cm(-1) and 4000-100cm(-1), respectively. The vibrational spectra were analysed and the observed fundamentals were assigned and analysed. The experimental wavenumbers were compared with the theoretical scaled vibrational wavenumbers determined by DFT methods. The Raman intensities were also determined with B3LYP/6-31G(d,p) method. The total electron density and molecular electrostatic potential surface of the molecule were constructed by using B3LYP/6-311++G(d,p) method to display electrostatic potential (electron+nuclei) distribution. The HOMO and LUMO energies were measured. Natural bond orbital analysis of primidone has been performed to indicate the presence of intramolecular charge transfer. The (1)H and (13)C NMR spectra were recorded and the chemical shifts of the molecule were calculated.
  Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 03/2013; 109C:282-297. · 2.10 Impact Factor
• Article: Conformational, vibrational, NMR and DFT studies of N-methylacetanilide.

  V Arjunan, R Santhanam, T Rani, H Rosi, S Mohan
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  ABSTRACT: A detailed conformational, vibrational, NMR and DFT studies of N-methylacetanilide have been carried out. In DFT, B3LYP method have been used with 6-31G(**), 6-311++G(**) and cc-pVTZ basis sets. The vibrational frequencies were calculated resulting in IR and Raman frequencies together with intensities and Raman depolarisation ratios. The dipole moment derivatives were computed analytically. Owing to the complexity of the molecule, the potential energy distributions of the vibrational modes of the compound are also calculated. Isoelectronic molecular electrostatic potential surface (MEP) and electron density surface were examined. (1)H and (13)C NMR isotropic chemical shifts were calculated and the assignments made are compared with the experimental values. The energies of important MO's of the compound were also determined from TD-DFT method.
  Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 11/2012; 104C:182-196. · 2.10 Impact Factor
• Article: Structural, vibrational, electronic investigations and quantum chemical studies of 2-amino-4-methoxybenzothiazole.

  V Arjunan, Arushma Raj, R Santhanam, M K Marchewka, S Mohan
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  ABSTRACT: Extensive vibrational investigations of 2-amino-4-methoxybenzothiazole have been carried out with FTIR and FT-Raman spectral techniques. The electronic structure of the molecule has been analysed by UV-Visible and NMR spectroscopies. The DFT studies were carried out with B3LYP and HF methods utilising 6-31G(d,p), 6-311++G(d,p) and cc-pVDZ basis sets to determine the structural, thermodynamical, vibrational, electronic characteristics of the compound and also to understand the electronic and steric influence of the methoxy amino groups on the skeletal frequencies. The mixing of the fundamental modes was determined with the help of total energy distribution (TED). The energies of the frontier molecular orbitals have also been determined. The kinetic and thermodynamic stability and chemical hardness of the molecule have been determined. Complete NBO analysis was also carried out to find out the intramolecular electronic interactions and their stabilisation energy. (1)H and (13)C NMR chemical shifts and the electronic transitions of the molecule are also discussed.
  Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 10/2012; 102C:327-340. · 2.10 Impact Factor
• Article: A comparative study on vibrational, conformational and electronic structure of 1,2-dimethyl-5-nitroimidazole and 2-methyl-5-nitroimidazole.

  V Arjunan, P Ravindran, R Santhanam, Arushma Raj, S Mohan
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  ABSTRACT: The FTIR and FT-Raman spectra of 1,2-dimethyl-5-nitroimidazole and 2-methyl-5-nitroimidazole have been recorded in the regions 4000-400 and 4000-100cm(-1), respectively. The conformational analyses were performed and the energies of the different possible conformers were determined. The geometry of different conformers of the compounds were optimised with B3LYP and B3PW91 methods using 6-311++G(∗∗) and aug-cc-pVTZ basis sets to characterise all stationary points as minima. The optimised structural parameters of the most stable conformer were used in the vibrational frequency calculations. The Raman activities were also determined with B3LYP method using 6-311++G(∗∗) basis sets. The force constants obtained from the B3LYP/6-311++G(∗∗) method have been utilised in the normal coordinate analysis. The temperature dependence of the thermodynamic properties heat capacity at constant pressure (C(p)), entropy (S) and enthalpy change (ΔH(0→T)) for both the compounds were also determined by B3LYP/6-311++G(∗∗) method. The total electron density and MESP surfaces of the molecules were constructed by NBO analysis using B3LYP/6-311++G(∗∗) method to display electrostatic potential (electron+nuclei) distribution, molecular shape, size, and dipole moments of the molecule. The electronic properties HOMO and LUMO energies were measured. The influences of nitro and methyl groups on the skeletal modes have been investigated.
  Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 06/2012; 97:176-88. · 2.10 Impact Factor
• Article: Structural characteristics and harmonic vibrational analysis of the stable conformer of 2,3-epoxypropanol by quantum chemical methods.

  V Arjunan, T Rani, R Santhanam, S Mohan
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  ABSTRACT: The FT-IR and FT-Raman spectra of H bond inner conformer of 2,3-epoxypropanol have been recorded in the regions 3700-400 and 3700-100cm(-1), respectively. The spectra were interpreted in terms of fundamentals modes, combination and overtone bands. The normal coordinate analysis was carried out to confirm the precision of the assignments. The structure of the conformers H bond inner and H bond outer1 were optimised and the structural characteristics were determined by density functional theory (DFT) using B3LYP and MP2 methods with 6-31G∗∗ and 6-311++G∗∗ basis sets. The vibrational frequencies were calculated in all these methods and were compared with the experimental frequencies which yield good agreement between observed and calculated frequencies. The electronic properties HOMO and LUMO energies were measured by time-dependent TD-DFT approach.
  Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 05/2012; 96:24-34. · 2.10 Impact Factor