Experimental IR, Raman, and UV-Vis Spectra DFT Structural and Conformational Studies: Bioactivity and Solvent Effect on Molecular Properties of Methyl-Eugenol.

Structural, conformational, and spectroscopic investigations of methyl-eugenol were made theoretically at the B3LYP-6-311++G**level. Experimental IR, Raman, and UV-vis spectra were investigated and analyzed in light of the computed quantities. Conformational analysis was carried out with the help of total energy vs. dihedral angle curves for different tops, yielding 21 stable conformers, out of which only two have energies below the room temperature relative to the lowest energy conformer. The effect of the solvent on different molecular characteristics was investigated theoretically. MEP and HOMO-LUMO analysis were carried out and barrier heights and bioactivity scores were determined. The present investigation suggests that the molecule has three active sites with moderate bioactivity. The solvent-solute interaction is found to be dominant in the vicinity of the methoxy moieties.

FTIR and Raman spectra, DFT and normal coordinate computations of 2,4,5- and 2,4,6-tri-fluoroanilines.

FTIR and Raman spectra of the 2,4,5- and 2,4,6-tri-fluoroaniline molecules have been reported. Density functional method has been employed to calculate the optimized geometrical parameters, atomic charges and vibrational frequencies. In addition, SQM force field method has also been employed to calculate potential energy distribution matrix. The observed and calculated IR and Raman spectra have been simulated. Each normal mode has been assigned using observed and calculated vibrational frequencies, IR and Raman intensities, depolarization ratios for the Raman lines, vector displacements and potential energy distributions. Optimized geometrical parameters, atomic charges and vibrational frequencies have been compared for the title molecules. The influences of presence of fluorine atoms to the geometries and normal modes of the aniline molecule have also been discussed.

FTIR and Raman spectra and SQM force field calculation for vibrational analysis of 2,3,4- and 2,3,6-tri-fluoro-anilines.

Raman and FTIR spectra for 2,3,4- and 2,3,6-tri-fluoro-aniline molecules have been recorded in the wavenumber regions 50-4000 and 400-4000 cm(-1) respectively. Measurement of depolarization ratios for the Raman lines for both the molecules has also been made. The HF with the basis set 6-31++G(d,p) and DFT with the basis sets 6-31++G(d,p) and 6-311++G(d,p) have been employed to carry out the molecular geometries, atomic charges and vibrational frequencies along with their IR and Raman intensities. Normal coordinate analysis method has also been employed to carry out the potential energy distributions (PEDs). The assignment of each normal mode has been made using observed and calculated frequencies, their IR and Raman intensities, depolarization ratios for the Raman lines and PEDs. The influences of fluorine atoms towards the geometries and normal modes of the aniline molecule have been discussed.

Infrared and ab initio studies of conducting molecules: 2,5-diamino-3,6-dichloro-1,4-benzoquinone.

2,5-Diamino-3,6-dichloro-1,4-benzoquinone has been synthesized by modifying the procedure reported in literature. Its IR spectrum has been recorded in the solid phase in the range 4000-400cm(-1). Ab initio calculations have been performed using Gaussian '03 program to compute optimized geometry, harmonic vibrational frequencies along with intensities in IR and Raman spectra and atomic charges at RHF/6-31+G*, B3LYP/6-31+G* and B3LYP/6-311++G** levels. To make vibrational analysis Gaussian View software was used. The optimized molecular structure is found to possess C2h point group symmetry. The observed IR frequencies have been assigned to different modes taking C2h molecular symmetry with the help of pictorial view of normal modes. From the magnitude of the observed frequencies corresponding to the NH2 stretching motions an indication of H-bonding is noticed. From geometrical parameters of the molecule it appears that two parallel sets of conjugated strands are formed in this molecule providing a route to conduct charges. The N-H bonds facing towards chlorine atoms are found to be shorter than those facing towards oxygen atoms indicating the presence of H-bonding between hydrogen atom of an NH2 group and carbonyl (quinoid) oxygen atom.

Quantum chemical determination of molecular geometries and interpretation of FTIR and Raman spectra for 2,4,5- and 3,4,5-tri-fluoro-benzonitriles.

Raman and FTIR spectra of 2,4,5- and 3,4,5-tri-fluoro-benzonitriles have been recorded in the regions 50-4000 cm(-1) and 400-4000 cm(-1), respectively. Measurement of depolarization ratios for the Raman lines has also been made. Optimized geometrical parameters, charge distributions and vibrational wavenumbers were calculated using ab initio quantum chemical Gaussian 03, Revision C.02 software. Each vibration has been assigned using observed wavenumbers in the IR and Raman spectra and their relative intensities which measured by normalizing the highest intensity, depolarization ratios of the Raman lines, the calculated frequencies and vector displacements with the help of GaussView software.

Ab initio determination of molecular geometries and vibrational frequencies of CX3 COOH (X=H, F, Cl, Br).

Using Gaussian 03 Revision C.02 version of the quantum chemical program ab initio and DFT computations have been carried out at the rhf/6-31+g*, b3lyp/6-31+g*, b3lyp/6-31++g** and b3lyp/6-311++g** levels to compute optimized geometries, harmonic vibrational frequencies along with intensities in IR and Raman spectra and atomic charges for the acetic (ethanoic) acid and its 1,1,1-tri-halo (fluoro, chloro and bromo) derivatives. The optimized molecular structures for all the four molecules are found to possess Cs point group symmetry. The symmetric stretching mode is found to have lowest magnitude of the three CX3 stretching modes for all the four molecules, whereas the symmetric deformation mode is found to have the lowest magnitude for EA and TFEA and the highest magnitude for TCEA and TBEA. The parallel rocking mode of the CX3 group is found to have lower magnitude than the perpendicular rocking mode for EA and TFEA where reverse is found for TCEA and TBEA. The modes of the COOH group are substituent sensitive except the OH stretching mode. Moreover, the maximum effect is found for the TFEA molecule. The CF3 group is found to have the characteristic frequencies as 235-505, 787, 1150-1190 and 1400 cm(-1) which are due to the modes delta s(CF3), nu s(CF3), nu as(CF3) and nu(C-CF3), respectively.

Structural and vibrational study of a neurotransmitter molecule: Dopamine [4-(2-aminoethyl) benzene-1,2-diol].

Structural and vibrational studies for the most stable conformer of dopamine {4-(2-Aminoethyl) benzene-1, 2-diol} have been carried out at the DFT/B3LYP/6-311++G** level using the Gaussian 09 software. The IR and Raman spectra have been recorded and analyzed in light of the computed vibrational parameters using the DFT and the PEDs computed with the help of the GAR2PED software. Some of the fundamentals have considerably changed frequencies in going from benzene to dopamine. Except the rocking and wagging modes of the NH2 group the other four modes are pure group modes. The rocking and wagging modes of the NH2 group show mixing with the other modes. The two OH stretching vibrations are highly localized modes. The Kekule phenyl ring stretching mode is found to remain almost unchanged. The HOMO-LUMO study suggests the existence of charge transfer within the molecule and the energy gap supports the pharmacological active property of the dopamine molecule. The NBO analysis has been carried out to understand the proper and improper hydrogen bonding.

Force field calculations and reassigments of Raman and IR frequencies of pyrazine-N,N'-dioxide.

Force field calculations have been carried out for the planar and non-planar modes of pyrazine-N,N'-O2 using the observed vibrational frequencies obtained from the IR and Raman spectral studies on pyrazine-N,N'-O2-h4 and pyrazine-N,N'-O2-d4 reported in the literature [D.A. Thornton, P.F.M. Verhoeven, G.M. Watkins, Herman O. Desseyn, Benjamin J. Van der Veken, Spectrochim. Acta 46A (1990) 1439]. The purpose of the present work is to determine force fields for the pyrazine-N,N'-O2 molecule and to present vibrational assignments for the observed IR and Raman frequencies to the fundamental modes, combination bands and overtones. The planar force field determined in the present case is expected to be better than that reported earlier [S. Szöke, G. Varsanyi, E. Baitz, Acta Chim. 53 (1967) 345] because of the inclusion of the observed frequencies due to pyrazine-N,N'-O2-d4 isotopomer. In addition, the non-planar force field for this molecule is reported for the first time.

Comparative structural and vibrational study of the four lowest energy conformers of serotonin.

A computational investigation of all possible lowest energy conformers of serotonin was carried out at the B3LYP/6-311++G** level. Out of the 14 possible lowest energy conformers, the first 4 conformers were investigated thoroughly for the optimized geometries, fundamental frequencies, the potential energy distributions, APT and natural charges, natural bond orbital (NBO) analysis, MEP, Contour map, total density array, HOMO, LUMO energies. The second third and fourth conformers are energetically at higher temperatures of 78, 94 and 312K respectively with respect to the first one. Bond angles and bond lengths do not show significant variations while the dihedral angles vary significantly in going from one conformer to the other. Some of the vibrational modes of the indole moiety are conformation dependent to some extent whereas most of the normal modes of vibration of amino-ethyl side chain vary significantly in going from one conformer to conformer. The MEP for the four conformers suggested that the sites of the maximum positive and negative ESP change on changing the conformation. The charges at some atomic sites also change significantly from conformer to conformer.

Force field calculations for 2-amino-5-chloro- and 2-amino-5-bromo-benzotrifluorides.

Force field calculations have been carried out for 2-amino-5-chloro- and 2-amino-5-bromo-benzotrifluorides using the earlier (Ref. of this article) reported IR and Raman spectra. As the frequencies of the corresponding modes for the C-Br and the C-Cl groups do not differ widely the two molecules are assumed to be isotopomers for the purpose of the force field calculations. The calculated and the observed frequencies match nicely for both the molecules. Consistent assignments have been proposed for the ring modes and the internal modes of the CF3 and the NH2 groups based on the potential energy distributions (PEDs), the IR and the Raman intensities and the depolarisation ratios of the Raman lines.

DFT-B3LYP computations of electro and thermo molecular characteristics and mode of action of fungicides (chlorophenols).

Density functional theoretical (DFT) calculations of the pesticides; 2-chlorophenol (2-CP), 2,4,6-trichlorophenol (TCP) and pentachlorophenol (PCP) have been carried out using 6-311++G** basis set available on Gaussian-09 software in order to optimize the molecular structures. The optimized geometry of the molecules has been found to possess Cs symmetry. The charge transfer phenomena occurring in the molecules have been exhibited by (HOMO-LUMO) analysis. The molecular ESP values and mappings of electron density iso-surface with the molecular electrostatic potential (MEP), have been carried out to achieve the information of the size, shape, charge density distribution and site of chemical reactivity of the molecules. Thermo molecular characteristics have been computed to achieve essential environmental influence on the activities of fungicides.

Investigation of crystal structure, vibrational characteristics and molecular conductivity of 2,3-dichloro-5,6-dicyno-p-benzoquinone.

Molecular geometries and vibrational spectra for the ground state of 2,3-dichloro-5,6-dicyno-p-benzoquinone (DDQ) and its anion (DDQ(-)) were computed using DFT method at the B3LYP level employing 6-311++G(d,p) basis set whereas for the first excited state (DDQ(∗)), these were calculated using TD-DFT at the B3LYP level employing the 6-311++G(d,p) basis set available with the Gaussian 09 package. The spectra have been experimentally investigated and the observed IR and Raman bands have been assigned to different normal modes on the basis of the calculated potential energy distributions (PEDs). XRD of single crystal has been investigated to determine molecular and crystal structures of DDQ. In order to elucidate the transfer of electrons, electronic structure and electronic absorption have been calculated with the TD-DFT method. Vibronic interaction and its role in the appearance of superconductivity in the DDQ, DDQ(-) and DDQ(∗) molecules have been investigated. The present XRD, molecular, electronic and vibronic studies indicate that mainly the ag C=O stretching and ring stretching modes participate in the charge transfer process.

Laser Raman and IR spectra and force fields for 2,4-dichlorobenzonitrile.

Raman spectrum of 2,4-dichlorobenzonitrile (2,4-DCBN) in powder form has been recorded in the region 50-4000 cm(-1) on a Jasco K-500 Raman spectrophotometer using the 488.0 nm radiation from an argon laser. FTIR spectra in the region 200-4000 cm(-1) have been recorded in KBr pellet and nujol mull on a Nicolet DX spectrometer. Using the observed Raman and IR frequencies, normal co-ordinate analysis has been carried out to support the vibrational analysis and to determine the planar and non-planar force fields.

Raman and IR studies and DFT calculations of the vibrational spectra of 2,4-Dithiouracil and its cation and anion.

Raman and FTIR spectra of solid 2,4-Dithiouracil (DTU) at room temperature have been recorded. DFT calculations were carried out to compute the optimized molecular geometries, GAPT charges and fundamental vibrational frequencies along with their corresponding IR intensities, Raman activities and depolarization ratios of the Raman bands for the neutral DTU molecule and its cation (DTU+) and anion (DTU-) using the Gaussian-03 software. Addition of one electron leads to increase in the atomic charges on the sites N1 and N3 and decrease in the atomic charges on the sites S8 and S10. Due to ionization of DTU molecule, the charge at the site C6 decreases in the cationic and anionic radicals of DTU as compared to its neutral species. As a result of anionic radicalization, the C5C6 bond length increases and loses its double bond character while the C4C5 bond length decreases. In the case of the DTU+ ion the IR and Raman band corresponding to the out-of-phase coupled NH stretching mode is strongest amongst the three species. The anionic DTU radical is found to be the most stable. The two NH out-of-plane bending modes are found to originate due to out-of-phase and in-phase coupling of the two NH bonds in the anion and cation contrary to the case of the neutral DTU molecule in which the out-of-plane bending motions of the two NH bonds are not coupled.

Experimental Raman and IR spectral and theoretical studies of vibrational spectrum and molecular structure of Pantothenic acid (vitamin B5).

Vibrational spectrum of Pantothenic acid has been investigated using experimental IR and Raman spectroscopies and density functional theory methods available with the Gaussian 09 software. Vibrational assignments of the observed IR and Raman bands have been proposed in light of the results obtained from computations. In order to assign the observed IR and Raman frequencies the potential energy distributions (PEDs) have also been computed using GAR2PED software. Optimized geometrical parameters suggest that the overall symmetry of the molecule is C1. The molecule is found to possess eight conformations. Conformational analysis was carried out to obtain the most stable configuration of the molecule. In the present paper the vibrational features of the lowest energy conformer C-I have been studied. The two methyl groups have slightly distorted symmetries from C3V. The acidic OH bond is found to be the smallest one. To investigate molecular stability and bond strength we have used natural bond orbital analysis (NBO). Charge transfer occurs in the molecule have been shown by the calculated highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energies. The mapping of electron density iso-surface with electrostatic potential (ESP), has been carried out to get the information about the size, shape, charge density distribution and site of chemical reactivity of the molecule.

Experimental and theoretical studies of vibrational spectrum and molecular structure and related properties of pyridoxine (vitamin B6).

Vibrational spectrum of pyridoxine has been investigated using experimental IR and Raman spectroscopic and density functional theory (DFT) methods. Vibrational assignments of the observed IR and Raman bands have been proposed in light of the results obtained from computations. In order to assign the observed IR and Raman frequencies the potential energy distributions (PEDs) have also been computed. Optimized geometrical parameters suggest that if the OH groups of the two methyl groups are replaced by H atoms the resulting molecule has Cs point group symmetry. To investigate molecular stability and bond strength we have used natural bond orbital analysis (NBO). Charge transfer occurs in the molecule have been shown by the calculated highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energies. The mapping of electron density iso-surface with electrostatic potential (ESP), has been carried out to get the information about the size, shape, charge density distribution and site of chemical reactivity of the molecule.

DFT study of conformational and vibrational characteristics of 2-(2-hydroxyphenyl)benzothiazole molecule.

The conformational and IR and Raman spectral studies of 2-(2-hydroxyphenyl)benzothiazole have been carried out by using the DFT method at the B3LYP/6-311++G(**) level. The detailed vibrational assignments have been done on the basis of calculated potential energy distributions. Comparative studies of molecular geometries, atomic charges and vibrational fundamentals of all the conformers have been made. There are four possible conformers for this molecule. The optimized geometrical parameters obtained by B3LYP/6-311++G(**) method showed good agreement with the experimental X-ray data. The atomic polar tensor (APT) charges, Mulliken atomic charges, natural bond orbital (NBO) analysis and HOMO-LUMO energy gap of HBT and its conformers were also computed.

Synthesis, characterization and quantum chemical investigation of molecular structure and vibrational spectra of 2,5-dichloro-3,6-bis-(methylamino)1,4-benzoquinone.

2,5-Dichloro-3,6-bis-methylamino-[1,4]benzoquinone has been synthesized by condensing methyl amine hydrochloride with chloranil in presence of condensing agent sodium acetate. FT-IR (4000-400 cm(-1)) and FT-Raman (4000-400 cm(-1)) spectral measurements of dmdb have been done. Ab initio and DFT (B3LYP/6-311+G(**)) calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies, infrared intensities and Raman activities. The optimized molecular structure of the compound is found to possess C2h point group symmetry. A detailed interpretation of the observed IR and Raman spectra of dmdb is reported on the basis of the calculated potential energy distribution. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using NBO analysis. The HOMO and LUMO energy gap reveals that the energy gap reflects the chemical activity of the molecule. The thermodynamic functions of the title compound have also been computed.

Vibrational studies of benzene, pyridine, pyridine-N-oxide and their cations.

IR and Raman spectra of pyridine and pyridine-N-oxide have been recorded and analyzed. The optimized molecular geometries, APT charges and vibrational characteristics for benzene, pyridine, pyridine-N-oxide and their cations have been computed using DFT method. Due to attachment of O atom at N site or removal of electron all the modes are affected in magnitudes. However, significant changes are noticed in their IR intensities, Raman activities and depolarization ratios of the Raman bands in going from pyridine to its N-oxide or in going from neutrals to their cations. It is interesting to note that in going from benzene to benzene cation charge redistribution takes place to reduce the symmetry from D6h to D2h. The calculated frequencies have been correlated with the experimental frequencies for the pyridine and pyridine-N-oxide molecules.

Theoretical DFT study on spectroscopic signature and molecular dynamics of neurotransmitter and effect of hydrogen removal.

Vibrational spectroscopic study has been made for the serotonin molecule and its deprotonated form. The Infrared and Raman spectra in optimum geometry of these two molecules are calculated using density functional theorem and the normal modes are assigned using potential energy distributions (PEDs) which are calculated using normal coordinate analysis method. The vibrational frequencies of these two molecules are reported and a comparison has been made. The effect of removal of the hydrogen atom from the serotonin molecule upon its geometry and vibrational frequencies are studied. Electronic structures of these two molecules are also studied using natural bond orbital (NBO) analysis. Theoretical Raman spectrum of serotonin at different exciting laser frequencies and at different temperatures are obtained and the results are discussed. Present study reveals that some wrong assignments had been made for serotonin molecule in earlier study.