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Arjunan V.,Kanchi Mamunivar Center for Post Graduate Studies | Sakiladevi S.,Ar Engineering College | Mythili C.V.,Rani Anna Government College for Women | Mohan S.,Hawasa University Main Campus
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2012

The FT-IR (4000-400 cm -1) and FT-Raman (4000-100 cm -1) spectral measurements and complete assignments of the observed spectra of 2-amino-4-methylbenzothiazole (2A4MBT) have been proposed. Ab initio and DFT calculations have been performed and the structural parameters of the compound were determined from the optimised geometry with 6-31G(d,p), 6-311++G(d,p) and cc-pVDZ basis sets and giving energies, harmonic vibrational frequencies, depolarisation ratios, IR intensities and Raman activities. 1H and 13C NMR spectra were recorded and 1H and 13C nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. UV-visible spectrum of the compound was also recorded and the electronic properties, such as HOMO, LUMO and band gap energies were measured by time-dependent DFT (TD-DFT) approach. The geometric parameters, energies, harmonic vibrational frequencies, IR intensities, Raman activities chemical shifts and absorption wavelengths were compared with the available experimental data of the molecule. The influences of methyl and amino groups on the skeletal modes and on the proton chemical shifts have been investigated. © 2011 Elsevier B.V. All rights reserved.


Arjunan V.,Kanchi Mamunivar Center for Post Graduate Studies | Kalaivani M.,Kanchi Mamunivar Center for Post Graduate Studies | Sakiladevi S.,Ar Engineering College | Carthigayan C.,Dr Br Ambedkar Polytechnic College | Mohan S.,Hawasa University Main Campus
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2012

N-(2,4-Dimethylphenyl)-2,2-dichloroacetamide (24DMPA) and N-(3,5-dimethylphenyl)-2,2-dichloroacetamide (35DMPA) of the configuration X yC 6H 5-yNHCOCHCl 2 (where, X = CH 3 and y = 2) were synthesised and an extensive spectroscopic investigations have been carried out. The ab initio and DFT studies were carried out with 6-31G** and cc-pVDZ basis sets to determine the structural, thermodynamical and vibrational characteristics of the compounds and also to understand the steric influence of methyl groups on the characteristic frequencies of amide (CONH) group. The most stable conformer has been determined by PES scan. Normal co-ordinate analysis has been carried out in an effort to provide mixing of the fundamental modes with the help of potential energy distribution (PED). The energies of the frontier molecular orbitals have been determined. Complete NBO analysis was also carried out to find out the intramolecular electronic interactions and their stabilisation energy. All the computed values are well agreed with the experimental data. © 2011 Elsevier B.V. All rights reserved.


Arjunan V.,Kanchi Mamunivar Center for Post Graduate Studies | Ravindran P.,Mahatma Gandhi Government Arts College | Balakrishnan K.,Avvm Sri Pushpam College | Santhanam R.,Kanchi Mamunivar Center for Post Graduate Studies | Mohan S.,Hawasa University Main Campus
Journal of Molecular Structure | Year: 2012

The FT-IR and FT-Raman spectra of 2-chloro-4-nitrotoluene and 4-chloro-2-nitrotoluene have been recorded in the regions 4000-400 and 4000-100 cm-1, respectively. The conformational analyses were performed and the energies of the different possible conformers were determined. The geometry of the most stable conformers of the compounds were optimised with B3LYP method using 6-31G**, 6-311++G** and cc-pVTZ basis sets. The optimised structural parameters of the most stable conformer were used in the vibrational frequency calculations. The Raman intensities were also determined with B3LYP method using cc-pVTZ basis set. 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 (Cp), entropy (S) and enthalpy change (ΔH0→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 using B3LYP/6-311++G ** method to display electrostatic potential (electron + nuclei) distribution. The electronic properties HOMO and LUMO energies were measured. The influences of chloro and nitro groups on the skeletal modes have been investigated. © 2012 Elsevier B.V. All rights reserved.


Arjunan V.,Kanchi Mamunivar Center for Post Graduate Studies | Balamourougane P.S.,PRIST University | Santhanam R.,Kanchi Mamunivar Center for Post Graduate Studies | Mohan S.,Hawasa University Main Campus
Journal of Molecular Structure | Year: 2012

The FT-IR and FT-Raman spectra of 4,5-dimethyl-1,3-dioxol-2-one have been recorded in the regions 4000-400 and 4000-100 cm-1, respectively. The geometry of compound was optimised with B3LYP method using 6-311++G, 6-31G and cc-pVTZ basis sets to characterise all stationary points as minima. The optimised structural parameters of the most stable geometry were used in the vibrational frequency calculations. 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 like heat capacity at constant pressure (Cp), entropy (S) and enthalpy change (ΔH0→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 methyl groups on the skeletal properties have been investigated. © 2012 Elsevier B.V. All rights reserved.


Arjunan V.,Kanchi Mamunivar Center for Post Graduate Studies | Rani T.,PRIST University | Santhanam R.,Kanchi Mamunivar Center for Post Graduate Studies | Mohan S.,Hawasa University Main Campus
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2012

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 3700-100 cm-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. © 2012 Elsevier B.V. All rights reserved.


Arjunan V.,Kanchi Mamunivar Center for Post Graduate Studies | Balamourougane P.S.,PRIST University | Kalaivani M.,Kanchi Mamunivar Center for Post Graduate Studies | Raj A.,Kanchi Mamunivar Center for Post Graduate Studies | Mohan S.,Hawasa University Main Campus
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2012

The FT-IR and FT-Raman spectra of 8-hydroxy-5-nitroquinoline have been recorded in the regions 4000-400 and 4000-100 cm-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 compound was optimised and the structural characteristics were determined by density functional theory (DFT) using B3LYP method with 6-31G, 6-311++G and cc-pVDZ 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 infrared and Raman spectra were also predicted from the calculated intensities. 1H and 13C NMR spectra were recorded and 1H and 13C nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. UV-Visible spectrum of the compound was recorded and the electronic properties HOMO and LUMO energies were measured by time-dependent TD-DFT approach. The influences of the nitro and hydroxy groups on the skeletal modes and on the proton chemical shifts have been investigated. © 2012 Elsevier B.V. All rights reserved.


Arjunan V.,Kanchi Mamunivar Center for Post Graduate Studies | Raj A.,Kanchi Mamunivar Center for Post Graduate Studies | Subramanian S.,Pondicherry Engineering College | Mohan S.,Hawasa University Main Campus
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2013

The FTIR and FT-Raman spectra of 1,2,4-benzenetricarboxylic-1,2-anhydride (BTCA) have been recorded in the range 4000-400 and 4000-100 cm-1, respectively. The complete vibrational assignments and analysis of BTCA have been performed. More support on the experimental findings was added from the quantum chemical studies performed with DFT (B3LYP, MP2, B3PW91) method using 6-311++G, 6-31G and cc-pVTZ basis sets. The structural parameters, energies, thermodynamic parameters, vibrational frequencies and the NBO charges of BTCA were determined by the DFT method. The 1H and 13C isotropic chemical shifts (δ ppm) of BTCA with respect to TMS were also calculated using the gauge independent atomic orbital (GIAO) method and compared with the experimental data. The delocalization energies of different types of interactions were determined. © 2013 Elsevier B.V. All rights reserved.


Arjunan V.,Kanchi Mamunivar Center for Post Graduate Studies | Raj A.,Kanchi Mamunivar Center for Post Graduate Studies | Santhanam R.,Kanchi Mamunivar Center for Post Graduate Studies | Marchewka M.K.,Institute of Low Temperature And Structure Research | Mohan S.,Hawasa University Main Campus
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2013

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. 1H and 13C NMR chemical shifts and the electronic transitions of the molecule are also discussed. © 2012 Elsevier B.V. All rights reserved.


Arjunan V.,Kanchi Mamunivar Center for Post Graduate Studies | Thillai Govindaraja S.,Bharathiar University | Subramanian S.,Pondicherry Engineering College | Mohan S.,Hawasa University Main Campus
Journal of Molecular Structure | Year: 2013

The stable geometry of the compound has been determined by conformational analysis. The relative stabilities of the different conformations were discussed. The complete vibrational assignment and analysis of the fundamental modes of the compound 2-bromo-3-nitroacetophenone (2B3NAP) were carried out using the experimental FTIR and FT-Raman data and quantum mechanical studies. The experimental vibrational frequencies were compared with the wavenumbers obtained theoretically from the DFT-B3LYP and B3PW91 calculations employing the standard 6-31G**, high level 6-311++G **, cc-pVTZ basis sets for optimised geometry of the compound. The potential energy distribution of the fundamental modes was also calculated by utilising Wilson's FG matrix method. The electronic properties, HOMO and LUMO energies were measured by time-dependent TD-DFT approach. The charges of the atoms by natural bond orbital (NBO) analysis were determined by B3LYP/6-311++G** method. The effect of NO2 and Br groups on the configuration of keto group and the skeletal vibrations have been discussed. © 2013 Elsevier B.V. All rights reserved.


Arjunan V.,Kanchi Mamunivar Center for Post Graduate Studies | Raj A.,Kanchi Mamunivar Center for Post Graduate Studies | Mythili C.V.,Rani Anna Government College for Women | Mohan S.,Hawasa University Main Campus
Journal of Molecular Structure | Year: 2013

Detailed structural and vibrational investigations of 5-benzimidazole carboxylic acid have been carried out with FTIR and FT-Raman spectral techniques. The electronic structure of the molecule has been analysed by 1H and 13C NMR spectroscopies. The DFT studies were carried out with B3LYP method utilising 6-31G**, 6-311++G** and cc-pVTZ basis sets to determine the structural, thermodynamical, vibrational, electronic characteristics of the compound and also to understand the electronic and steric influence of the carboxylic group on the skeletal frequencies. Complete NBO analysis was also carried out to find out the intramolecular electronic interactions and their stabilisation energy. The extreme limits of the electrostatic potential is +1.435e × 10-2 and -1.435e × 10-2. The frontier orbital energy gap in the case of 5BICA is found to be 5.2742 eV. In 5BICA molecule, the lone pair donor orbital, nN→ πCN * interaction between the N1 lone pair and C2N3 antibonding orbital is seen to give a strong stabilisation of 43.32 kJ mol-1. © 2012 Elsevier B.V. All rights reserved.

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