Experimental vibrational spectra (Raman,infrared) and DFT calculations on monomeric and dimeric structures of 2‐ and 6‐bromonicotinic acid

In this work, the Fourier transform infrared and Raman spectra of 2‐bromonicotinic acid and 6‐bromonicotinic acid (abbreviated as 2‐BrNA and 6‐BrNA, C₆H₄BrNO₂) have been recorded in the region 4000–400 and 3500–50 cm⁻¹. The optimum molecular geometry, normal mode wavenumbers, infrared intensities and Raman scattering activities, corresponding vibrational assignments and intermolecular hydrogen bonds were investigated with the help of B3LYP density functional theory (DFT) method using 6‐311++G(d,p) basis set. Reliable vibrational assignments were made on the basis of total energy distribution (TED) calculated with scaled quantum mechanical (SQM) method. From the calculations, the molecules are predicted to exist predominantly as the C1 conformer. Copyright © 2009 John Wiley & Sons, Ltd.     

Crystal and molecular structure of 2‐amino‐5‐chloropyridinium hydrogen selenate—its IR and Raman spectra,DFT calculations and physicochemical properties

The new organic‐inorganic salt, 2‐amino‐5‐chloropyridinium hydrogen selenate, has been synthesised and characterised by means of FT‐IR, FT‐Raman and single crystal X‐ray crystallography. Its vibrational spectra have been discussed on the basis of quantum chemical DFT calculations using the B3LYP/6‐31G(d,p) approach. The crystal and molecular structures have been compared and the role of the intermolecular interactions in this crystal has been analysed. The N HO interactions between the hydrogen atoms of the organic cation and oxygen atoms of hydrogen selenate anion determine the supramolecular arrangement in three‐dimensional space. The possible application of the studied composite material as a Raman laser has been discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Molecular structure and vibrational spectra of 3 (or 4 or 6)‐methyl‐5‐nitro‐2‐pyridinethiones: FT‐IR,FT‐Raman and DFT quantum chemical calculations

IR and Raman spectra (RS) of polycrystalline 3‐(or 4 or 6)‐methyl‐5‐nitro‐2‐pyridinethione have been measured and analyzed by means of density functional theory (DFT) quantum chemical calculations. The B3LYP/6‐311G(2d,2p) approach has been applied for both the thiol and thione tautomers due to the possibility of the formation of these two thiole forms. Molecular structures of these compounds have been optimized starting from different molecular geometries of the thiol group and thione group. Two conformations of the 2‐mercaptopyridine, trans and cis, have been taken into account. It was shown that the studied compounds appear in the solid state in the thione form. The effect of the hydrogen‐bond formation in the studied compounds has been considered. Copyright © 2008 John Wiley & Sons, Ltd.     

FT‐Raman,FT‐IR spectra and DFT calculations on monomeric and dimeric structures of 5‐fluoro‐ and 5‐chloro‐salicylic acid

The experimental and theoretical study on the structures and vibrations of 5‐fluoro‐salicylic acid and 5‐chloro‐salicylic acid (5‐FSA and 5‐ClSA, C₇H₅FO₃ and C₇H₅ClO₃) is presented. The Fourier transform infrared spectra (4000–400 cm⁻¹) and the Fourier transform Raman spectra (4000–50 cm⁻¹) of the title molecules in the solid phase were recorded. The molecular structures, vibrational wavenumbers, infrared intensities, Raman intensities and Raman scattering activities were calculated for a pair of molecules linked by the intermolecular O H···O hydrogen bond. The geometrical parameters and energies of 5‐FSA and 5ClSA were obtained for all eight conformers/isomers from density functional theory (DFT) (B3LYP) with 6‐311++G(d,p) basis set calculations. The computational results identified the most stable conformer of 5‐FSA and 5‐ClSA as the C1 form. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The spectroscopic and theoretical results were compared with the corresponding properties for 5‐FSA and 5‐ClSA monomers and dimer of C1 conformer. The optimized bond lengths, bond angles and calculated wavenumbers showed the best agreement with the experimental results. Copyright © 2010 John Wiley & Sons, Ltd.     

IR,Raman and SERS spectra of ethyl salicylate

The IR and Raman spectra of ethyl salicylate were recorded and analyzed. The surface enhanced Raman scattering (SERS) spectrum was recorded in a silver colloid. The vibrational wavenumbers of the compound have been computed using the Hartree‐Fock/6‐31G* basis. The direction of charge transfer contribution to SERS has been discussed from the frontier orbital theory. The presence of methyl modes in the SERS spectrum indicates the nearness of the methyl group to the metal surface and the presence of ring vibrations and out‐of‐plane ring modes in the SERS spectrum suggests a flat orientation of the molecule on the silver surface. The first hyperpolarizability is calculated and the calculated molecular geometry has been compared with the reported similar structures. Copyright © 2009 John Wiley & Sons, Ltd.     

Experimental and theoretical investigation of vibrational spectra of copper phthalocyanine: polarized single‐crystal Raman spectra,isotope effect and DFT calculations

The IR‐ and Raman spectra of copper phthalocyanine (CuPc), as well as the isotopic wavenumber shifts upon ¹⁵N substitution in CuPc, were investigated experimentally and theoretically. The symmetry of molecular vibrations was determined using polarized Raman spectra of an oriented CuPc single crystal. Density functional theory (DFT) calculations were used for the detailed assignment of different bands in the vibrational spectra of CuPc. Theoretically predicted geometry, wavenumbers and isotopic shifts are in a very good agreement with the experimental values. A comparison of experimentally obtained isotopic shifts with theoretical predictions allowed us to reveal some characteristic features of normal vibrations of CuPc molecule. Copyright © 2009 John Wiley & Sons, Ltd.     

FT‐IR,FT‐Raman and DFT calculations of 3‐{[(4‐fluorophenyl)methylene]amino}‐2‐phenylquinazolin‐4(3H)‐one

Fourier transform (FT)‐Raman and Fourier transform infrared (FT‐IR) spectra of 3‐{[(4‐fluorophenyl)methylene]amino}‐2‐phenylquinazolin‐4(3H)‐one were recorded and analyzed. The vibrational wavenumbers of the title compound were computed using the B3LYP/6‐31G* basis and compared with the experimental data. The prepared compound was identified by NMR and mass spectra. The simultaneous IR and Raman activation of the CO stretching mode shows a charge transfer interaction through a π‐conjugated path. The first hyperpolarizability and infrared intensities are reported. The assignments of the normal modes are done by potential energy distribution (PED) calculations. Copyright © 2008 John Wiley & Sons, Ltd.     

Crystal and molecular structure of 2‐aminopyridinium‐ 4‐hydroxybenzenosulfonate—IR and Raman spectra,DFT calculations and physicochemical properties

A new organic–organic salt, 2‐aminopyridinium‐4‐hydroxybenzenosulfonate, has been synthesised and characterised by means of FT‐IR and FT‐Raman spectroscopies, differential scanning calorimetry (DSC) and single crystal X‐ray crystallography. Its vibrational spectra have been discussed on the basis of quantum chemical density functional theory (DFT) calculations using the B3LYP/6‐31G(d,p) approach. The role of the intermolecular interactions in this crystal is analysed. The N HċċċO interactions between the hydrogen atoms of the pyridinium cation and oxygen atoms of hydroxybenzenosulfonate anion built the supramolecular arrangement in three‐dimensional space. Copyright © 2008 John Wiley & Sons, Ltd.     

Calculation of transition intensities for torsional vibrations in IR and Raman spectra of dihydroxybenzenes

We present the calculated intensity distribution for bands and lines in torsional IR and Raman spectra of dihydroxybenzenes. The calculations were based on calculated matrix elements for the components of the dipole moment and the polarizability tensor. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 598–603, September–October, 2007.     

Quantum-chemical calculations of the structure,vibrational spectra,and torsional and inversion potentials of methylcarbamate

We present results of ab initio and DFT calculations of the structure, potential functions of the methyl group internal rotation and the amino group inversion, and vibrational frequencies and intensities in IR and Raman spectra of methylcarbamate. The calculations were carried out using different basis sets in the HF, MP2, and DFT/B3LYP approximations. The influence of both the basis set size and the allowance for electronic correlation on peculiarities of the structure of the amino group in methylcarbamate has been analyzed. It is shown that the B3LYP/6-311++G(2d, p) and B3LYP/cc-pVDZ calculations reproduce highly accurately experimental geometric parameters of methylcarbamate. Parameters of torsional and inversion potentials and characteristics of vibrational spectra calculated in different approximations show satisfactory agreement with experimental values. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 349–357, May–June, 2009.     

基于密度泛函理论的莫西沙星振动光谱研究

莫西沙星作为第四代氟喹诺酮类抗生素被大量的使用,在人体以及家畜体内会有药物残留,危害每个人的生命健康。为了避免人体二次摄入,能够快速检测肉制品中是否含有莫西沙星残留的方法尤为重要。为此,采用振动光谱技术结合密度泛函理论方法为莫西沙星的振动光谱检测与鉴定提供基础数据,为其在药品检测领域的应用提供参考。具体研究内容和结果如下：第一步以密度泛函理论为基础（DFT）,构建莫西沙星分子空间结构,利用B3LYP/6-311+G(d)基组优化结构并计算其理论拉曼光谱与红外光谱。理论计算结果发现莫西沙星分子在3 700~2 800与1 800~400 cm-1范围内具有明显的拉曼与红外活性,前者主要是官能团上键的振动,后者为指纹区上键的振动。由于两种光谱信息互补的优越性,首先通过对比理论拉曼光谱与红外光谱,标记出同时具有两种或只具有一种振动活性的振动峰频率,结合Gaussian view显示莫西沙星分子中每个键对应的振动频率进行全面的归属,同时给出莫西沙星分子的键长、键角和二面角等空间结构参数。第二步通过实验测量了莫西沙星（Moxifloxacin,MXF）的自然拉曼光谱（NRS）与红外光谱（IR）。理论计算结果误差由频率校正因子0.973修正,再与实验数据相比较,峰值波数相差大多在0~10 cm-1范围内,计算结果与实验数据基本一致,该结果为莫西沙星的振动光谱检测与鉴定提供基础数据,为其在药品检测领域的应用提供参考。     

FT‐IR,FT‐Raman,and computational calculations of 4‐chloro‐2‐(3‐chlorophenyl carbamoyl)phenyl acetate

FT‐IR and FT‐Raman spectra of 4‐chloro‐2‐(3‐chlorophenylcarbamoyl) phenyl acetate were studied. Vibrational wavenumbers and corresponding vibrational assignments were examined theoretically using the Gaussian03 set of quantum chemistry codes and the normal modes are assigned by potential energy distribution (PED) calculations. Simultaneous IR and Raman activation of the CO stretching mode shows the charge transfer interaction through a π‐conjugated path. Optimized geometrical parameters of the title compound are in agreement with the reported values. Analysis of the phenyl ring modes shows that C C stretching mode is equally active as strong bands in both IR and Raman, which can be interpreted as the evidence of intramolecular charge transfer via conjugated ring path and is responsible for hyperpolarizability enhancement leading to nonlinear optical activity. The red‐shift of the NH‐stretching wavenumber in the infrared spectrum from the computed wavenumber indicates the weakening of the NH bond resulting in proton transfer to the neighboring oxygen atom. Copyright © 2009 John Wiley & Sons, Ltd.     

FT‐IR,FT‐Raman,SERS spectra and computational calculations of 4‐ethyl‐N‐(2′‐hydroxy‐5′‐nitrophenyl)benzamide

Fourier transform infrared (FT‐IR) and FT‐Raman spectra of 4‐ethyl‐N‐(2′‐hydroxy‐5′‐nitrophenyl)benzamide were recorded and analyzed. A surface‐enhanced Raman scattering (SERS) spectrum was recorded in silver colloid. The vibrational wavenumbers and corresponding vibrational assignments were examined theoretically using the Gaussian03 set of quantum chemistry codes. The red shift of the NH stretching wavenumber in the infrared spectrum from the computational wavenumber indicates the weakening of the NH bond resulting in proton transfer to the neighboring oxygen atom. The simultaneous IR and Raman activation of the CO stretching mode gives the charge transfer interaction through a π‐conjugated path. The presence of methyl modes in the SERS spectrum indicates the nearness of the methyl group to the metal surface, which affects the orientation and metal molecule interaction. The first hyperpolarizability and predicted infrared intensities are reported. The calculated first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive subject for future studies of nonlinear optics. Optimized geometrical parameters of the title compound are in agreement with reported structures. Copyright © 2009 John Wiley & Sons, Ltd.     

Hydrogen bonding in the pyrimidine/ formamide system: a concentration‐dependent Raman and DFT study

High‐resolution Raman spectra of pyrimidine (PD) and formamide (FA) mixtures with different compositions recorded in the ring breathing region of PD (ν₁ ∼ 991 cm⁻¹) are presented. The dilution of PD with FA leads to the appearance of a new band at ν₁′ ∼ 994 cm⁻¹, which is assigned to hydrogen‐bonded PD:FA species. From a quantitative analysis of the concentration‐dependent Raman spectra, the average number of FA molecules in the first solvation sphere of PD is determined as being equal to 2. This value is supported by density functional theory (DFT) calculations: a symmetric 1:2 complex is the most stable species among various hydrogen‐bonded PD:FA clusters with stoichiometries ranging from 1:1 to 1:4. A qualitative explanation for the blue shift of the ν₁ mode upon complexation is given. Additionally, we have observed not only similarities but also some differences with respect to the PD:water system. Copyright © 2010 John Wiley & Sons, Ltd.     

FT‐IR,FT‐Raman and SERS spectra of anilinium sulfate

The FT‐IR and FT‐Raman spectra of anilinium sulfate were recorded and analyzed. The surface‐enhanced Raman scattering (SERS) was recorded from a silver electrode. The vibrational wavenumbers of the compound have been computed using the Hartree‐Fock/6‐31G* basis and compared with the experimental values. The molecule is adsorbed on the silver surface with the benzene ring in a tilted orientation. The presence of amino and sulfate group vibrations in the SERS spectrum reveal the interaction between amino and sulfate groups with the silver surface. The direction of the charge transfer contribution to SERS has been discussed from the frontier orbital theory. Copyright © 2009 John Wiley & Sons, Ltd.     

Experimental and theoretical studies on corals. I. Toward understanding the origin of color in precious red corals from Raman and IR spectroscopies and DFT calculations

An attempt to explain the origin of the vivid red color in precious pink and red corals was undertaken. Raman and IR spectroscopies were applied to characterize white, pink and red corals. The position of the Raman signal near 1500 cm⁻¹ of some corals and pearls was associated by several authors with the presence of the mixture of all‐trans‐polyenic pigments, containing 6–16 conjugated CC bonds or β‐carotenoids. This hypothesis was examined theoretically by performing extensive B3LYP‐DFT calculations of vibrational spectra of the model polyenic compounds. The B3LYP/6‐311++G** predicted positions of the dominating Raman mode depend on the number of CC units (Cn parameter) and can be accurately predicted for larger systems from a simple nonlinear fit. The DFT‐predicted Raman activities of these modes are extremely sensitive to Cn, and sharply increase with the number of double bonds. This implies a presence of only—two to three polyenes differing slightly in the number of CC units as the source of color in pink and red corals. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopy of acetic acid monomer and dimers isolated in solid argon

Acetic acid (AA) monomer and its dimers were studied by means of Raman spectroscopy combined with the matrix isolation technique. All fundamental bands of CH₃COOH monomer were identified, including the CH₃ torsional mode. Additionally, three overtone or combination modes were observed as a result of their enhanced intensities by Fermi resonance (FR). Twenty bands of the cyclic dimer (C_2h) were identified and assigned, among which appear all intermolecular modes. Bands due to two different higher energy forms of the dimer were also identified. The experimental assignments are supported by ab initio calculations. Copyright © 2011 John Wiley & Sons, Ltd.     

Vibrational spectroscopic studies and DFT calculations of 4‐fluoro‐N‐(2‐hydroxy‐4‐nitrophenyl)benzamide

Fourier transform infrared (FT‐IR) and FT‐Raman spectra of 4‐fluoro‐N‐(2‐hydroxy‐4‐nitrophenyl)benzamide were recorded and analyzed. The vibrational wavenumbers and corresponding vibrational assignments were examined theoretically using the Gaussian03 set of quantum chemistry codes. The red‐shift of the NH‐stretching wavenumber in the infrared (IR) spectrum from the computed wavenumber indicates the weakening of the NH bond resulting in proton transfer to the neighboring oxygen atom. The simultaneous IR and Raman activation of the CO‐stretching mode gives the charge transfer interaction through a π‐conjugated path. Copyright © 2008 John Wiley & Sons, Ltd.     

Hydrogen bonding in different pyrimidine–methanol clusters probed by polarized Raman spectroscopy and DFT calculations

We report on the hydrogen bonding between pyrimidine (Pd) and methanol (M) as H‐donor in this study. Hydrogen bonds between pyrimidine and methanol molecules as well as those between different methanol molecules significantly influence the spectral features at high dilution. The ring‐breathing mode ν₁ of the reference system Pd was chosen as a marker band to probe the degree of hydrogen bonding. Polarized Raman spectra in the region 970–1020 cm⁻¹ for binary mixtures of (pyrimidine + methanol) at 28 different mole fractions were recorded. A Raman line shape analysis of the isotropic Raman line profiles at all concentrations revealed three distinct spectral components at mole fractions of Pd below 0.75. The three components are attributed to three distinct groups of species: ‘free Pd’ (pd), ‘Pd with low methanol content’ (pd1) and ‘Pd with high‐methanol content’ (pd2). The two latter species differ considerably in the pattern and the strengths of the hydrogen bonds. The results of density functional theory calculations on structures and vibrational spectra of neat Pd and eight Pd/M complexes with varying methanol content support our interpretations of the experimental results. A nice spectra–structure correlation for the different cluster subgroups was obtained, similar to earlier results obtained for Pd and water. Apart from N···H and O···H hydrogen bonds between pyrimidine and methanol, O···H hydrogen bonds formed among the methanol molecules in the cluster at high methanol content also play a crucial role in the interpretation of the experimental results. Copyright © 2010 John Wiley & Sons, Ltd.     

XRD studies,vibrational spectra,and molecular structure of 1H‐imidazo [4,5‐b]pyridine based on DFT quantum chemical calculations

The molecular structures and vibrational properties of 1H‐imidazo[4,5‐b]pyridine in its monomeric and dimeric forms are analyzed and compared to the experimental results derived from the X‐ray diffraction (XRD), infrared (IR), and Raman studies. The theoretical data are discussed on the basis of density functional theory (DFT) quantum chemical calculations using Lee–Yang–Parr correlation functional (B3LYP) and 6‐31G(d,p) basis. This compound crystallizes in orthorhombic structure, space group Pna2₁(C_2v⁹) and Z = 4. The planar conformation of the skeleton and presence of the N H···N hydrogen bond was found to be characteristic for the studied system. The temperature dependence of IR and Raman modes was studied in the range 4–294 K and 8–295 K, respectively. The normal modes, which are unique for the imidazopyridine derivatives are identified. Copyright © 2009 John Wiley & Sons, Ltd.