Vibrational spectroscopy of resveratrol

In this article the authors deal with the experimental and theoretical interpretation of the vibrational spectra of trans-resveratrol (3,5,4'-trihydroxy-trans-stilbene) of diverse beneficial biological activity. Infrared and Raman spectra of the compound were recorded; density functional calculations were carried out resulting in the optimized geometry and several properties of the molecule. Based on the calculated force constants, a normal coordinate analysis yielded the character of the vibrational modes and the assignment of the measured spectral bands.     

三核钼簇合物H[H2O]3[Mo3O(OAc)I3Cl6]的合成分子结构及红外光谱归属的研究

本文报道MoCl3.3H2O与乙酸作用生成三核钼簇合物H[H2O]3[Mo3O(OAc)3Cl6]的反应, 并用X射线单晶结构分析方法测定了簇合物的晶体结构, 结晶学参数. 结构分析结果表明该化合物阴离子为单氧帽等边三角形三核钼簇合阴离子, Mo-Mo平均距离2.569埃.对簇骼单元[Mo3O(μ-Cl)3Cl3]^2^+进行简正坐标分析. 从理论上对振动光谱谱带进行了归属. 10条IR谱带的观测和计算频率的平均偏差为1.15%. 本文讨论了特征谱带(包括金属键)的归属和力常数的合理性.     

A DFT study on the vibrational spectroscopy of protoporphyrin IX

Infrared and Raman spectra of protoporphyrin IX were recorded. DFT quantum chemical calculations were performed. Optimised molecular geometry, electric charge distribution, vibrational force constants were computed. The normal coordinate analysis and the scaling of the force constants yielded all the necessary data for the simulation of the infrared and Raman spectra and the potential energy distribution calculations. The result was the interpretation of all vibrational modes of the molecule. Conclusions were drawn from the difficulties arisen during the assignment of the vibrational spectra of such large molecules.     

Analysis of vibrational spectra of L-alanylglycine based on density functional theory calculations

FT Raman and IR spectra of the crystallized biologically active molecule, L-alanylglycine (L-Ala-Gly) have been recorded and analyzed. The equilibrium geometry, bonding features and harmonic vibrational frequencies of L-Ala-Gly have been investigated with the help of B3LYP density functional theory (DFT) method. The calculated molecular geometry has been compared with the experimental data. The assignments of the vibrational spectra have been carried out with the help of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The optimized geometry shows the non-planarity of the peptide group of the molecule. Potential energy surface (PES) scan studies has also been carried out by ab initio calculations with B3LYP/6-311+G** basis set. The red shifting of NH3+ stretching wavenumber indicates the formation of N-H...O hydrogen bonding. The change in electron density (ED) in the sigma* antibonding orbitals and E2 energies have been calculated by natural bond orbital analysis (NBO) using DFT method. The NBO analysis confirms the occurrence of strong intermolecular hydrogen bonding in the molecule.     

Intramolecular charge delocalization and nonlinear optical properties of push-pull chromophore 1-(4-N,N-dimethylaminopyridinium) acetic acid bromide monohydrate from vibrational spectra

FT-Raman and FT-IR spectra of the nonlinear optical crystal 1-(4-N,N-dimethylaminopyridinium) acetic acid bromide monohydrate have been recorded and analyzed. The equilibrium geometry, vibrational wavenumbers and the first order hyperpolarizability of the crystal have been calculated with the help of density functional theory computations. The assignments of the vibrational spectra have been carried out with the help of Scaled Quantum Mechanic force field theory. Optimized geometry gives the charge transfer interaction of the pyridine ring and the amino group in the electron-donor side of the nonlinear optic chromophore. Electron–phonon coupling and O–H?O interactions in making the molecule nonlinear optical active have been analyzed based on the vibrational spectral features. The Natural Bond Orbital analysis confirms the occurrence of strong intermolecular O–H?O hydrogen bonding.     

Experimental and theoretical vibrational study of silyl trifluoromethanesulfonate, CF3SO2OSiH3

Infrared and Raman spectra were obtained for liquid silyl trifluoromethanesulfonate, a silylating agent of limited stability. The molecular geometry was optimized by means of density functional theory and M?ller-Plesset second order perturbation theory methods, using different basis sets. The optimized structure presents a gauche conformation, similar to that adopted by methyl trifluoromethanesulfonate, which was determined experimentally a short time ago. The wavenumbers for the normal modes of vibration and the corresponding force constants were also calculated, facilitating the interpretation of the vibrational data. The harmonic force constants given by theory were scaled to reproduce adequately the experimental wavenumbers.     

All-trans- and t,T,t,C,t,T,t-deca-1,3,5,7,9-Pentaenes: Ab Initio Structures,Vibrational Analyses,and Some Regularities in the Series of Related Molecules

Total geometry optimization and calculation of the force constants for all-transand t,T,t,C,t,T,tdeca-1,3,5,7,9-pentaene were carried out at the ab initio, HF/6-31G level. The HF/6-31G//HF/ 6-31G force fields were modified using empirical scale factors transferred from trans-buta-1,3-diene augmented by an additional scale factor for the central formal carbon-carbon double bond coordinates (determined previously for all-trans-hexa-1,3,5-triene). The total number of scale factors was seven. The vibrational problems for both decapentaenes were solved using the respective scaled HF/6-31G//HF/6-31G force field. Infrared intensities and Raman activities were calculated from the unscaled HF/6-31G//HF/6-31G force fields. Complete assignment of all the fundamental vibrational frequencies is given. Geometrical parameters, vibrational frequencies and force constants are compared with the corresponding values of buta-1,3-diene, hexa-1,3,5-triene and octa-1,3,5,7-tetraene. Regularities in the properties of this molecular series are discussed. Special attention is given to the possibility of using the vibrational spectra for detection of distortions from the regular trans structure of these oligoenes.     

Fourier-transform infrared and Raman spectra of cysteine dichloride cadmium(II) anion DFT: B3LYP/3-21G(d) structural and vibrational calculations

The cysteine dichloride cadmium(II) potassium was synthesized and the structural analysis was carried out through the following methods: determination of the C, H, N, S and O contents, thermogravimetry, infrared and Raman spectra. Assuming Cd-S, Cd-O (O-carboxilate) and Cd-N bonds, several hypothetical structures were calculated by means DFT: B3LYP/3-21G(d) quantum mechanical method. The calculations shows that the Cd-S and Cd-N central bonds are favoured in the anion complex formation [Cd(Cys)Cl2]-, being the stabilization energy 55.52 kcal mol(-1) lower than isotopomers with Cd-S and Cd-O central bonds. Features of the infrared and Raman spectra confirm the theoretical structural prediction. Full assignment of the vibrational spectra is proposed based on the DFT procedure, and in order to confirm the C-H, N-H, C-C, C-N, Cd-N, Cd-S and Cd-Cl stretching and the HNH and HCH bending, a normal coordinate analysis based on local symmetry force field for -SC(H2)C-, -CdN(H2)C- and -SCd(Cl2)N- fragments was carried out.     

Theoretical and experimental vibrational spectrum study of 4-hydroxybenzoic acid as monomer and dimer

Theoretical calculations on the molecular geometry and the vibrational spectrum of 4-hydroxybenzoic acid were carried out by the Density Functional Theory (DFT/B3LYP) method. In addition, IR and Raman spectra of the 4-hydroxybenzoic acid in solid phase were newly recorded using them in conjunction the experimental and theoretical data (including SQM calculations), a vibrational analysis of this molecular specie was accomplished and a reassignment of the normal modes corresponding to some spectral bands was proposed. The geometries of monomers and dimers in gas phase were optimized using the DFT B3LYP method with the 6-31G*, D95** and 6-311++G** basis sets. Also, both the vibrational spectra recorded and the results of the theoretical calculations show the presence of one stable conformer for the 4-hydroxybenzoic acid cyclic dimer. The B3LYP/6-31G* method was used to study the structure for cyclic dimer of 4-hydroxybenzoic acid and for a complete assignment our results were compared with results of the cyclic dimer of benzoic acid. A scaled quantum mechanical analysis was carried out to yield the best set of harmonic force constants. The formation of the hydrogen bond was investigated in terms of the charge density by the AIM program and by the NBO calculations.     

Vibrational spectra and ab initio analysis of tert-butyl,trimethylsilyl, and trimethylgermyl derivatives of 3,3-dimethylcyclopropene III. 3,3-Dimethyl-1-(trimethylsilyl)cyclopropene

The experimental Raman and IR vibrational spectra of 3,3-dimethyl-1-(trimethylsilyl)cyclopropene in the liquid phase were recorded. Total geometry optimisation was carried out at the HF/6-31G* level and the HF/6-31G*//HF/6-31G* force field was computed. This force field was corrected by scale factors determined previously (using Pulay's method) for correction of the HF/6-31G*//HF/6-31G* force fields of 3,3-dimethylbutene-1, 1-methyl-, 1,2-dimethyl-, and 3,3-dimethylcyclopropene. The theoretical vibrational frequencies calculated from the scaled quantum mechanical force field and the theoretical intensities obtained from the quantum mechanical calculation were used to construct predicted spectra and to perform the vibrational analysis of the experimental spectra.     

Ab Initio Equilibrium Geometry and Vibrational Spectroscopic Study of 25,26,27,28-tetrahydroxycalix[4]arene

The aim of this work was to present a comprehensive vibrational spectroscopic study of 25,26,27,28-tetrahydroxycalix[4]arene. For this purpose, quantum chemical calculations were carried out at the ab initio HF/4-31G* level, as a consequence of the great size of the molecule. In the frame of these calculations, the symmetry of the molecule was investigated. Trying C 4v , C 2v , and C s symmetries as input, the geometry optimization, however, pointed to the C 2 configuration. In the latter case, all the calculated vibrational frequencies were greater than zero, and therefore the equilibrium geometry could be identified. Medium and far infrared as well as Raman spectra of the compound were measured. On the basis of the calculated force constants and geometric parameters, normal coordinate analysis was applied for the interpretation of the experimental vibrational spectra. Problems arose with the choice of the internal coordinates of the molecule, which are important from the point of view of the internal macrocycle ("lower rim") of the molecule. On the basis of the theory of redundant coordinates, a program was written for choosing the coordinates of this 16-membered cycle. Full interpretation of the vibrational fundamentals of the compound is presented. Several force constant matrix elements have surprisingly high values. As a result of the normal coordinate analysis, the relative rigidity of the lower rim was concluded. Ab initio calculations and assignment of the vibrational spectra of 25,26,27,28-tetrahydroxycalix[4]arene based on the calculations are presented.     

Ab-initio molecular geometry and normal coordinate analysis of pyrrolidine molecule.

The molecular geometry of pyrrolidine was quantum mechanically calculated using the split valence 6-31G** basis set. Electron correlation energy has been computed employing MP2 method. The molecule showed an envelope form puckered structure with inter-plane angle of 36.4 degrees and has a total energy of -132976.80 kcal mol(-1) of which a -464.86 kcal mol(-1) electron correlation energy. The twist form of the molecule showed a twist angle of 10.2 degrees from planarity and has a total energy of -132976.05 kcal mol(-1) involving -464.097 kcal mol(-1) electron correlation energy. The normal coordinates of the molecule were theoretically analyzed on the basis of the Cs point symmetry of the envelope form. Using initial set of force constants obtained from the ab-initio calculations the fundamental vibrational frequencies were computed. The IR and laser Raman spectra of Pyrrolidine molecules were measured. All the observed vibrational bands including combination bands and overtones were assigned to normal modes with the aid of the potential energy distribution values obtained from normal coordinate calculations. The molecular force field was obtained by refining the initial set of force constants using the least square fit method. The molecular force field was determined by refining the initial set of force constants using the least square fit method instead of using the less accurate scaling factor methods. The determined molecular force field has produced simulated frequencies best match to the observed values. The low frequency molecular out-of-plane deformation modes were observed in both infrared and Raman spectra at 298 and 163 cm(-1). The barrier of ring twisting estimated from the observed ring out-of-plane vibrational mode at 163 cm(-1) was found 3.1 kcal mol(-1).     

Effect of hydrogen bonding and cooperativity on stretching force constants of formamide

Stretching force constants for formamide and its seven associated species involving two to four molecules hydrogen-bonded through linear and cyclic configurations and 10 structures containing formamide hydrogen-bonded with one to five water molecules are reported. Since ab initio calculations are rather inconvenient to perform on such big clusters and are time-consuming, CNINDO MO calculations were carried out using the gradient method. The results demonstrate, on the one hand, the feasibility of semiempirical calculations for the evaluation of trends in force constants for big clusters where generally ab initio calculations become much involved and, on the other hand, explain the effect of hydrogen bonding and cooperativity on force constants and vibrational spectra of biologically important systems composed of formamide in the condensed phase and its aqueous solutions. The C?O and N? H stretching force constants are found to reduce significantly on hydrogen bonding. The reduction in force constant is further enhanced when two cyclic dimers become associated through a linear hydrogen bond. The results indicate justification for the stabilization of the formamide structure with two cyclic dimers hydrogen-bonded together. The reduction in the force constants on hydrogen bonding also reflect the cooperativity contribution. The C?O and C? N stretching force constants for the structures corresponding to formamide in liquid and aqueous solution phases are in agreement with the experimental vibrational frequencies reported.     

Vibrational spectra and normal coordinate analysis of plant growth regulator 1-naphthalene acetamide

FT Raman and IR spectra of the biologically active molecule, 1-naphthalene acetamide (NA) have been recorded and analyzed. The equilibrium geometry, bonding features and harmonic vibrational wavenumbers of NA have been calculated with the help of B3LYP density functional theory (DFT) method. The assignments of the vibrational spectra have been carried out with the help of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The downshifting of NH₂ stretching wavenumber indicates the formation of intermolecular N–H?O hydrogen bonding. The NBO analysis confirms the occurrence of strong intermolecular hydrogen bonding in the molecule.     

Structure and vibrational spectra of dinitromethane and trinitromethane

The molecular geometries of dinitromethane and trinitromethane were optimized and their harmonic force fields were calculated by the DFT/B3LYP method. The force fields obtained made it possible to interpret reliably the vibrational spectra of dinitromethane, trinitromethane and a number of isotopomers of trinitromethane. Some general conclusions on geometry and vibrational spectra of the molecules under study are made. The hybrid density functional method used is shown to predict the reliable structural parameters and vibrational frequencies for polynitromethanes.     

Vibrational spectra and DFT study of anticancer active molecule 2-(4-Bromophenyl)-1H-benzimidazole by normal coordinate analysis

FT-IR and FT-Raman spectra of the 2-(4-Bromophenyl)-1H-benzimidzole were recorded and analyzed in the solid phase. The optimized molecular geometry, the vibrational wavenumbers, the infrared intensities and the Raman scattering activities were calculated by using Hartree-Fock and density functional method (B3LYP) with 6-31G(d,p) basis set. The potential surface scan study was carried out for the conformation of theoretical structure. Detailed interpretation of the vibrational spectra had been carried out with the aid of the normal coordinate analysis. Chemical interpretation of hyperconjugative interaction was done by natural bond orbital analysis.     

FTIR and FT Raman, molecular geometry, vibrational assignments, ab initio and density functional theory calculations for 1,5-methylnaphthalene

The FTIR and FT Raman vibrational spectra of 1,5-methylnaphthalene (1,5-MN) have been recorded using Brunker IFS 66 V Spectrometer in the range 3600-10 cm(-1) in the solid phase. A detailed vibrational spectral analysis has been carried out and assignments of the observed fundamental bands have been proposed on the basis of peak positions and relative intensities. The Optimized molecular geometry, harmonic frequencies, electronic polarizability, atomic charges, dipole moment, rotational constants and several thermodynamic parameters in the ground state were calculated using ab initio Hartree Fock (HF) and density functional B3LYP methods (DFT) with 6-311++ G(d) basis set. With the help of different scaling factors, the observed vibrational wavenumbers in FTIR and FT Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wavenumbers in the expected range. The results of the calculations were applied to simulated infrared and Raman spectra of the title compound which showed excellent agreement with the observed spectra.     

Vibrational analysis of chlorinated methylphosphonic acid and its anions

The vibrational spectra (IR and Raman) of CH₂ClPO₃H₂ and of its anions in solutions of H₂O and D₂O are reported. The IR spectra of the solid dibasic sodium and potassium salts, the solid normal and O-deuterated monobasic sodium and potassium salts and of the solid normal and O-deuterated acid are discussed. Symmetry and internal stretching force constants, stretch-stretch interactions and potential energy distributions are obtained from normal coordinate analysis of CH₂C1PO₃H₂, CH₂ClPO₃H^? and CH₂C1PO₃^2?, and the calculated and observed frequencies for O-deuterated acid and monobasic anion are compared.     

Normal coordinate and infrared band intensities of trichloronitromethane and trichloroacetate ions

Laser Raman and IR spectra in the region 50–3000 cm⁻¹ for trichloronitromethane and trichloroacetate ions were recorded. All observed vibrational bands have been assigned to normal modes. Normal coordinate analyses of these molecules have been carried out in the valence force-field approximation. A set of force constants was obtained leading to good agreement between observed and calculated frequencies. The relative displacements of the atoms resulting from normal coordinate calculations were used to compute the IR band intensity of each mode by the CNDO/2-MO procedure. The intensity calculations confirmed the assignments and supported the calculated force constants.