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.     

Experimental and theoretical FT‐IR and FT‐Raman spectroscopic analysis of N1‐methyl‐2‐chloroaniline

In this work, the experimental and theoretical vibrational spectra of N1‐methyl‐2‐chloroaniline (C₇H₈NCl) were studied. FT‐IR and FT‐Raman spectra of the title molecule in the liquid phase were recorded in the region 4000–400 cm^?1 and 3500–50 cm^?1, respectively. The structural and spectroscopic data of the molecule in the ground state were calculated by using density functional method (B3LYP) with the 6‐311++G(d,p) basis set. The vibrational frequencies were calculated and scaled values were compared with experimental FT‐IR and FT‐Raman spectra. The observed and calculated frequencies are found to be in good agreement. 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. ¹³C and ¹H NMR chemical shifts results were compared with the experimental values. The optimized geometric parameters (bond lengths and bond angles) were given and are in agreement with the corresponding experimental values of aniline and p‐methyl aniline. Copyright © 2008 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.     

Infrared and Raman Spectra,conformations, ab initio calculations and spectral assignments of 1,3‐disilabutane (SiH3CH2SiH2CH3)

Raman spectra of 1,3‐disilabutane (SiH₃CH₂SiH₂CH₃) as a liquid were recorded at 293 K and as a solid at 78 K. In the Raman cryostat at 78 K an amorphous phase was first formed, giving a spectrum similar to that of the liquid. After annealing to 120 K, the sample crystallized and large changes occurred in the spectra since more than 20 bands present in the amorphous solid phase vanished. These spectral changes made it possible to assign Raman bands to the anti or gauche conformers with confidence. Additional Raman spectra were recorded of the liquid at 14 temperatures between 293 and 137 K. Some Raman bands changed their peak heights with temperature but were countered by changes in linewidths, and from three band pairs assigned to the anti and gauche conformers, the conformational enthalpy difference Δ_confH(gauche–anti) was found to be 0 ± 0.3 kJ mol⁻¹ in the liquid. Infrared spectra were obtained in the vapor and in the liquid phases at ambient temperature and in the solid phases at 78 K in the range 4000–400 cm⁻¹. The sample crystallized immediately when deposited on the CsI window at 78 K, and many bands present in the vapor and liquid disappeared. Additional infrared spectra in argon matrixes at 5 K were recorded before and after annealing to temperatures 20–34 K. Quantum chemical calculations were carried out at the HF, MP2 and B3LYP levels with a variety of basis sets. The HF and DFT calculations suggested the anti conformer as the more stable one by ca 1 kJ mol⁻¹, while the MP2 results favored gauche by up to 0.4 kJ mol⁻¹. The Complete Basis Set method CBS‐QB3 gave an energy difference of 0.1 kJ mol⁻¹, with anti as the more stable one. Scaled force fields from B3LYP/cc‐pVQZ calculations gave vibrational wavenumbers and band intensities for the two conformers. Copyright © 2007 John Wiley & Sons, Ltd.     

Infrared and Raman spectroscopic studies of the charge localization in one‐dimensional organic metals (DMtTTF)2X (X = ReO4, ClO4) with regular organic stacks

A novel selective synthesis of the unsymmetrically substituted tetrathiafulvalene dimethyltrimethylene‐tetrathiafulvalene (DMtTTF) is described together with its electrocrystallization to the known conducting mixed‐valence ClO₄^– and ReO₄^– salts. Infrared (IR) and Raman spectra of the two isostructural quasi‐one‐dimensional cation radical salts (DMtTTF)₂X (X = ReO₄^–, ClO₄^–) are investigated as a function of temperature (T = 5–300 K). At ambient temperature, these salts show metallic‐like properties and below T_ρ = 100–150 K, they undergo a smeared transition to semiconducting state. To study this charge localization, we measured temperature dependence of polarized IR reflectance spectra (700–16 000 cm^–1) and Raman spectra (150–3500 cm^–1, excitation λ = 632.8 nm) of single crystals. For both compounds, the Raman data and especially the bands related to the C=C stretching vibration of the DMtTTF molecule show that the charge distribution on molecules is uniform down to the lowest temperatures. Similarly, IR data confirm that down to the lowest temperatures, there is neither charge ordering nor important modification of the electronic structure. However, the temperature dependence of Raman spectra of both salts reveals a regime change at about 150 K. Additionally, using Density Functional Theory (DFT) methods, the normal vibrational modes of the neutral DMtTTF⁰ and cationic DMtTTF⁺ species and also their theoretical IR and Raman spectra were calculated. The theoretical data were compared with the experimental IR and Raman spectra of neutral DMtTTF⁰ molecule. Copyright © 2013 John Wiley & Sons, Ltd.     

Raman,infrared, SERS and theoretical study of 3‐(1‐phenylpropan‐2‐ylamino) propanenitrile,fenproporex

Infrared, Raman and surface‐enhanced Raman scattering (SERS) spectra of 3‐(1‐phenylpropan‐2‐ylamino)propanenitrile (fenproporex) have been recorded. Density functional theory (DFT) with the B3LYP functional was used for optimizations of ground state geometries and simulation of Raman and SERS vibrational spectra of this molecule. Bands of the vibrational spectra were assigned in detail. The comparison of SERS spectra obtained by using colloidal silver and gold nanoparticles with the corresponding Raman spectrum reveals enhancement and shifts in bands, suggesting a possible partial charge‐transfer mechanism in the SERS effect. Information about the orientation of fenproporex on the nanometer‐sized metal structures is also obtained. Copyright © 2011 John Wiley & Sons, Ltd.     

DFT,FT‐Raman,FT‐IR and NMR studies of 2‐fluorophenylboronic acid

The experimental and theoretical vibrational spectra of 2‐fluorophenylboronic acid (2fpba) were studied. The Fourier transform Raman and Fourier transform infrared spectra of the 2fpba molecule were recorded in the solid phase. The structural and spectroscopic analysis of the molecule was carried out by using Hartree‐Fock and density functional harmonic calculations. For the title molecule, only one form was found to be the most stable structure, by using B3LYP level with the 6‐31++G(d,p) basis set. Selected experimental bands were assigned and characterized on the basis of the scaled theoretical wavenumbers by their total energy distribution (TED). The ¹H and ¹³C nuclear magnetic resonance (NMR) chemical shifts of the 2fpba molecule were calculated using the Gauge‐Invariant‐ atomic orbital (GIAO) method in DMSO solution using IEF‐PCM model and compared with the experimental data. Finally, geometric parameters, vibrational wavenumbers and chemical shifts were compared with available experimental data of the molecule. Copyright © 2009 John Wiley & Sons, Ltd.     

Vibrational spectroscopic studies,conformations and ab initio calculations of 1,2‐bis(trifluorosilyl)ethane (SiF3CH2CH2SiF3)

Infrared spectra of 1,2‐bis(trifluorosilyl)ethane (SiF₃CH₂CH₂SiF₃) were obtained in the vapour and liquid phases, in argon matrices and in the solid phase. Raman spectra of the compound as a liquid were recorded at various temperatures between 293 and 270 K and spectra of an apparently crystalline solid were observed. The spectra revealed the existence of two conformers (anti and gauche) in the vapour, liquid and in the matrix. When the vapour was chock‐frozen on a cold finger at 78 K and annealed to 150 K, certain weak Raman bands vanished in the crystal. The vibrational spectra of the crystal demonstrated mutual exclusion between IR and Raman bands in accordance with C_2h symmetry. Intensity variations between 293 and 270 K of pairs of various Raman bands gave ΔH(gauche—anti) = 5.6 ± 0.5 kJ mol⁻¹ in the liquid, suggesting 85% anti and 15% gauche in equilibrium at room temperature. Annealing experiments indicate that the anti conformer also has a lower energy in the argon matrices, is the low‐energy conformer in the liquid and is also present in the crystal. The spectra of both conformers have been interpreted, and 34 anti and 17 gauche bands were tentatively identified. Ab initio and density functional theory (DFT) calculations were performed giving optimized geometries, infrared and Raman intensities and anharmonic vibrational frequencies for both conformers. The conformational energy difference derived in CBS‐QB3 and in G3 calculations was 5 kJ mol⁻¹. 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.     

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.     

Raman and IR studies of TaWO5.5, ASbWO6 (A = K,Rb, Cs,Tl), and ASbWO6·H2O (A = H,NH4, Li,Na) pyrochlore oxides

Raman and infrared (IR) spectra of defect pyrochlores TaWO_5.5, NH₄SbWO₆·H₂O, HSbWO₆·H₂O, LiSbWO₆·H₂O, NaSbWO₆·H₂O, KSbWO₆, RbSbWO₆, CsSbWO₆, and TlSbWO₆ were measured. The obtained spectra are discussed using the factor group approach for the cubic Fd‐3m space group, and assignment of bands to respective motions of atoms is proposed. Our results show that the phonon properties of the pyrochlores are strongly affected by disorder, and therefore Raman and IR spectroscopies are very useful tools in studying disorder in this family of compounds. In particular, our studies have shown that in these ionic conductors disorder at sites occupied by NH , H⁺, or alkali‐metal ions decreases with increasing size and mass of these ions. Copyright © 2010 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.     

Experimental and theoretical structure and vibrational analysis of ethyl trifluoroacetate,CF3CO2CH2CH3

The molecular structure and conformational properties of ethyl trifluoroacetate, CF₃CO₂CH₂CH₃, were determined in the gas phase by electron diffraction, and vibrational spectroscopy (IR and Raman). The experimental investigations were supplemented by ab initio (MP2) and DFT quantum chemical calculations at different levels of theory. Experimental and theoretical methods result in two structures with C_s (anti–anti) and C₁ (anti–gauche) symmetries, the former being slightly more stable than the latter. The electron‐diffraction data are best fitted with a mixture of 56% anti–gauche and 44% anti–anti conformers. The conformational preference was also studied using the total energy scheme, and the natural bond orbital scheme. Also, the infrared spectra of CF₃CO₂CH₂CH₃ are reported for the gas, liquid and solid states, as is the Raman spectrum of the liquid. The comparison of experimental averaged IR spectra of C_s and C₁ conformers provides evidence for the predicted conformations in the IR spectra. Harmonic vibrational wavenumbers and scaled force fields have been calculated for both conformers. Copyright © 2009 John Wiley & Sons, Ltd.     

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.     

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.     

2-巯基噻二唑的拉曼、红外光谱、DFT计算和简正振动分析

采用B3LYP混合泛函和6-311G基函数组,并对重原子和轻原子使用离散函数和极化函数,利用密度泛函理论计算了2-巯基噻二唑的分子振动频率。实验测量了2-巯基噻二唑分子的拉曼、红外光谱,以实验频率为标准对分子内力场进行了标度,采用简正振动分析方法得到了各振动模的势能分布,从而对该分子的振动频率归属做出了全面指认。     

Polarised IR and Raman spectra of non‐centrosymmetric Na3Li(MoO4)2· 6H2O crystal—a new Raman laser material

Polarised IR and Raman spectra of Na₃Li(MoO₄)₂· 6H₂O single crystal were measured. Discussion of the results is based on the factor group approach for the trigonal R 3c(C_3v⁶) space group with Z = 2. The assignment of the observed bands was performed on the basis of their polarisation behaviour and literature data. The obtained results for the spontaneous Raman scattering were used in the analysis of the stimulated Raman spectra of the material studied—a new Raman laser crystal. The promoting modes of the stimulated effect were identified. Copyright © 2009 John Wiley & Sons, Ltd.     

DFT simulations and vibrational analysis of FTIR and FT‐Raman spectra of 2‐amino‐4,6‐dihydroxypyrimidine

This work deals with the vibrational spectroscopy of 2‐amino‐4,6‐dihydroxy pyrimidine (ADHP) by means of quantum chemical calculations. The mid‐ and far FTIR and FT‐Raman spectra were measured in the condensed state. The fundamental vibrational wavenumbers and intensity of vibrational bands were evaluated using density functional theory (DFT) with the standard B3LYP/6‐311 + G** methods and basis set combinations, and were scaled using various scale factors, which yielded good agreement between the observed and calculated wavenumbers. The vibrational spectra were interpreted with the aid of normal coordinate analysis based on the scaled density functional force field. The results of the calculations were applied to simulate the infrared and Raman spectra of the title compound, which showed excellent agreement with the observed spectra. Copyright © 2008 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.     

Gas‐phase structure and new vibrational study of methyl trifluoroacetate (CF3C(O)OCH3)

The molecular structure of methyl trifluoroacetate (CF₃C(O)OCH₃) has been determined in the gas phase from electron‐diffraction data supplemented by ab initio (MP2) and DFT calculations using different basis sets. Experimental data revealed an anti conformation with a dihedral angle θ (CCOC) = 180°. Quantum mechanical calculations indicate the possible existence of two conformers, differing by a rotation about the C(O) O bond. The global minimum represents a C_s‐symmetric structure in which the CF₃ group has the anti orientation with respect to the CH₃ group, but there is another potential minimum, much higher in energy, representing a C_s‐symmetric structure with a cis conformation. The preference for the anti conformation was studied using the total energy scheme and the natural bond orbital (NBO) partition scheme. Additionally, the total potential energy has been deconvoluted using a six‐fold decomposition in terms of a Fourier‐type expansion, showing that the electrostatic and steric contributions are dominant in stabilizing the anti conformer. Infrared spectra of CF₃C(O)OCH₃ were obtained for the gaseous and liquid phases, while the Raman spectrum was recorded for the liquid phase. Harmonic vibrational frequencies and a scaled force field have been calculated, leading to a final root mean‐square deviation of 9 cm⁻¹ when comparing experimental and calculated frequencies. Copyright © 2009 John Wiley & Sons, Ltd.