Polarized Infrared and Raman Spectra and Ab-Initio Calculations of 2-(Methylthio)Benzothiazole

Abstract

The infrared spectra of 2-(methylthio)benzothiazole have been measured from 4000 to 180 cm^?1 for liquid and polycrystalline samples, polarized spectra of oriented films have also been obtained. the Raman spectra of polycrystalline and liquid samples have been investigated. the structural parameters, energies and vibrational frequencies have been calculated from ab-initio RHF calculations using the 6-31G?? basis set for various conformations. a detailed assignment of most of the observed bands has been proposed on the basis of the infrared dichroism, Raman polarization data and frequency calculations.     

Polarized Infrared and Raman Spectra of 2(3H)-Benzoxazolone

Abstract

The infrared spectra of 2(3H)-benzoxazolone have been measured from 4000 to 180 cm^?1. The polarized spectra of single crystals have been also obtained. The Raman spectra of polycrystalline samples and solutions have been recorded and the polarization of many lines has been determined. On the basis of the i.r. dichroism, Raman spectra and correlative arguments most of the fundamental vibrations have been assigned.     

Vibrational Assignment of N-Phenylphthalimide and 15N-Phenylphthalimide

Abstract

The i.r. spectra of N-phenylphthalimide and ¹⁵N-phenylphthalimide have been measured in 4000–100 cm^?1 frequency range as KBr and polyethylene pellets and as chloroform solutions. The Raman spectra (4000–50) cm^?1 of microcrystalline powder of the of the same compounds have also been investigated.

A detailed assignment of most of the observed frequencies has been proposed on the basis of the group vibrational concept, isotopic shift data and analogies with the spectra of related molecules. Some literature data have been discussed and some frequencies are reassigned.     

Assignments of Carbon-Sulphur Vibrations by Selenation: An FT-IR and FT-Raman Study on 1, 3, 5-Trithiacyclohexane

Abstract

The IR and Raman spectra of 1, 3, 5-trithiacyclohexane (1) and 1, 3, 5-triselenocyclohexane (2) have been recorded with FT-instrumentation within 3500–100 cm^?l, and the C-S vibrations of 1 have been reviewed by comparing its spectra with those of 2. The IR and Raman spectra slightly differ from those previously reported and some vibrations, previously assigned to C-H modes in 1on the basis of NCT calculations, are reassigned to C-S modes on the basis of the selenation effect. “Selenation” has proved to be a very simple and effective tool in recognizing carbon-sulfur vibrations both in IR and Raman. The Raman peaks due to carbon-chalcogen vibrations are less intense in 1 than in 2, according to the higher polarizability of the selenium atom.     

Ab Initio Calculations and Raman and SERS Spectral Analyses of Amphetamine Species

Abstract

For the first time, the differences between the spectra of amphetamine and amphetamine-H⁺ and between different conformers are thoroughly studied by ab initio model calculations, and Raman and surface-enhanced Raman spectroscopy (SERS) spectra are measured for different species of amphetamine. The spectra of amphetamine and amphetamine-H⁺ samples were obtained and assigned according to a comparison of the experimental spectra and the ab initio MO calculations, performed using the Gaussian 03W program (Gaussian, Inc., Pittsburgh, PA). The analyses were based on complete geometry minimization of the conformational energy of the S-plus-amphetamine molecule and the S-plus-amphetamine-H⁺ ion. The harmonic frequency calculations provide information about the characteristic features of the Raman spectra and the nature of the bonding in the molecule. It is concluded that vibrational bands from salt anions with internal bonds (sulfates, hydrogen phosphates, etc.) need to be taken into account when employing these spectra for identification purposes. These results also show how Raman spectroscopy can assist the forensic community in drug profiling studies. Furthermore, because their spectra are different, discrimination between the free and protonated forms of amphetamine salts can be observed. Here, we provide evidence for this difference and show experimentally how it has been overseen.     

Vibrational Spectra of 4-Benzoylpiridine and the 18O Substituted Derivative

Abstract

Infrared and Raman spectra of 4-benzoylpiridine (4BP) and its ¹⁸O substituted derivative have been recorded in the solid and in the molten state. Polarized Raman spectra in the molten state have also been measured. The assignment of the vibrational bands is performed on the basis of isotopic shifts, group vibrational concept and polarization features of the normal modes. The previous assignment of the in- and out-of-plane deformations of the carbonyl group and the fundamentals below 700 cm^?1 are questioned and corrected.     

Molecular Dynamics simulations of borate glasses

Abstract

The results of Molecular Dynamics simulations of borate glass (B₂O₃) using three-particle interactions are presented. These calculations yield a glass consisting of randomly connected BO₃ triangles. Infrared and Raman spectra have been calculated and compared with experimental spectra. The calculated infrared spectra show two main bands, one at 650 cm^?1 and one at 1250 cm^?1, in agreement with experiment. The Raman spectra reproduce the experimental peak at 805 cm^?1 but the peak width is a factor of ten too large. Apparently, the simulated glasses have less short range order than the laboratory glasses.     

15N Isotopic Effects on the Raman Spectra of Tribromoacetamide

Abstract

¹⁵N-Tribromoacetamide has been synthesized with an isotopic content of 99, 4%, its Raman spectra have been recorded in the range 4.000–50 cm^?1. The isotopic shifts arising from ¹⁵N have been determined and interpreted. We have assigned the vibrational spectra of Br₃CCONH₂ and some overtones, combinations and difference bands. The molecular structure of tribromoacetamide has been studied employing the Ab Initio teoretical calculations and the Teller - Redlich isotopic product rule has been applied by assuming these geometrical parameters:

rCN = 1.4623 Å, rCC = 1.6014 Å, rBrC = 1.9468 Å, rCO = 1.2144 Å, rNH = 1.0292 Å, C-C-Br = 108.83320, C-C-0:118.2440, C-C-N:120.4137, C-N-H:110.45930     

Raman Spectroscopic Study of the Orientation of Polystyrene in a Stretched Film and in an Adsorbed Film

Abstract

Polarized Raman scattering spectra and surface enhanced Raman scattering spectra have been recorded from a thin film of a stretched polystyrene and from an adsorbed thin layer of polystyrene on silver surface, respectively. Comparison of intensities of the Raman line near 786 cm^?1 indicates that the aromatic rings are perpendicular to the surface in polystyrene which deposited onto silver from a very dilute solution.     

Density functional theory calculations and vibrational spectra of p‐bromonitrobenzene

FT‐IR and FT‐Raman spectra of p‐bromonitrobenzene (p‐BNB) have been recorded in the region 4000–400 cm⁻¹ and 4000–50 cm⁻¹, respectively. The molecular structure, geometry optimization, vibrational wavenumbers have been investigated. The spectra were interpreted with the aid of normal coordinate analysis based on the density functional theory (DFT) using the standard B3LYP/6‐31G method and basis set combination and was scaled using multiple scale factors yielding good agreement between observed and calculated wavenumbers. The results of the calculations are applied to simulate infrared and Raman spectra of the title compound which showed reasonable agreement with the observed spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Vibrational Assignment of 2-Benzoyl Pyridine and its 18O Labelled Isomer

Abstract

Vibrational spectra of 2-benzoyl pyridine and 2-benzoyl pyridine-¹⁸O have been recorded in the solid and molten state in the infrared (4000–100 cm^?1) and in the Raman (4000–50 cm^?1). Polarized Raman spectra in the molten state have also been measured. The assignment of the vibrational bands is performed using the group vibrational concept, isotopic shifts and polarization features of the normal modes.     

Vibrational Spectra and Assignments for 3,4-Dibromothiophene

Abstract

The infrared spectrum of 3,4-dibromothiophene has been studied from 4000 to 200 cm^?1. The Laser Raman spectrum has also been recorded and depolarization values have been measured. An assignment of the 21 fundamental vibrations is proposed based on group frequency correlations, Raman polarization data and comparison with the spectra of parent and some halogeno-substituted molecules.     

Raman Spectroscopic Characterization of the Alkaloid Dihydrochelerytrine Extracted from Roots of Zanthoxylum stelligerum (Turcz)

ABSTRACT

Raman spectroscopy has been used successfully in the identification of the alkaloid dihydrochelerytrine due to the assignment of specific key marker bands in the region between 1000 and 1600 cm^?1. The Raman spectrum obtained from the crude hexane extract of the roots of Zanthoxylum stelligerum, and excited with 1064 nm, provides very good molecular information, as can be seen by the comparison between the Raman spectra of the standard dihydrochelerytrine and the crude extract, where the keymarker bands are present in both spectra.     

Spectroscopic properties of spinacine – an active component of ginseng (Panax ginseng) and spinach (Spinacia oleracea)

ABSTRACT

The molecular structures and vibrational properties of spinacine in its monomeric and dimeric forms are analyzed and compared to the experimental results derived from the infrared and Raman studies. The theoretical data are discussed on the basis of density functional theory quantum chemical calculations using the Lee–Yang–Parr correlation functional. The characteristic vibrations of the imidazopyridine double-ring systems in spinacine containing compounds were identified and characterized. The sequence of bands corresponding to spinacine contains the infrared or Raman lines observed at about 1612, 1307, 1250, 730, and 530?cm^?1. The occurrence of these bands in the spectra of a plant, its extracts or pharmaceuticals confirms the presence of the imidazopyridine skeleton in these substances. The analyses of extracts of ginseng roots and spinach leaves were performed using infrared spectroscopy. The wavenumbers and integral intensities of the observed bands were used to identify components of the phenylpropanoid pathway in the extracts and to prove the presence of spinacine in these natural products. The spectra of other compounds containing the imidazopyridine unit have been analyzed.     

Calculation of absorption and resonance Raman cross sections of ClO2 in the gas‐phase and in solution: including Duschinsky effects

The time‐correlation function formalism has been used to calculate resonance Raman cross sections, excitation profiles, and electronic absorption spectra of the OClO molecule in the gas‐phase and in different solvents like cyclohexane, chloroform, and water. The multidimensional time domain integrals that arise in these calculations have been evaluated for the case in which an X²B₁ òA₁ electronic transition takes place between displaced‐distorted‐rotated harmonic potential energy surfaces. Ab initio calculations have been performed to provide the spectroscopic constants required for the evaluation of these integrals. The calculated absorption spectra and resonance Raman cross sections have been compared with the experimental results. Copyright © 2009 John Wiley & Sons, Ltd.     

The Infrared and Raman Spectra of 4-Phenylpyridine and Its Hofmann Type Complexes.

Abstract

The Infrared and Raman spectra of 4-Phenylpyridine are reported for the first time in the 4000-400cm^?1 range. Vibrational assignments have been made for fundamental modes on the basis of frequency shifts of coordinated legend, infrared and Raman band contours and comparisons with the assignments for related molecules. The infrared spectra of M (4-Phenylpyridine) Ni(CN)₄ complexes (M=Mn, Ni or Cd) are reported. Their structure consists of polymeric layers of [M-Ni(CN)₄]_∞ with the 4-phenylpyridine molecules bound to metal (M), similar to the structure found in Hoffmann type host complexes.     

MgB2 and AlB2 at high pressures

We have studied the effect of pressure on vibrational and electronic properties of MgB₂ and AlB₂ by ab initio calculations and Raman spectroscopy. The comparison between the calculations and the Raman data puts the common assignment of a broad spectral feature near 600 cm^?1 in MgB₂ to the E _2g phonon into question. At variance with MgB₂ the Raman spectra of AlB₂ exhibit a well-defined E _2g mode indicating that the anomalous Raman spectrum encountered in MgB₂ is not related to the metallicity of the samples nor is it intrinsic to crystals of the AlB₂ structure type. A theoretical estimate of the pressure dependence of T _c in MgB₂ shows that the experimentally observed decrease of T _c under pressure is predominantly due to phonon frequency shifts.     

Molecular structure,NMR and vibrational spectral analysis of 2,4‐difluorophenol by ab initio HF and density functional theory

Quantum chemical calculations of energies, geometries and vibrational wavenumbers of 2,4‐difluorophenol (2,4‐DFP) were carried out by using ab initio HF and density functional theory (DFT/B3LYP) methods with 6‐311G(d,p) as basis set. The optimized geometrical parameters obtained by HF and DFT calculations are in good agreement with related molecules. The best level of theory in order to reproduce the experimental wavenumbers is the B3LYP method with the 6‐311G(d,p) basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. A detailed interpretation of the infrared and Raman spectra of 2,4‐DFP is also reported. The entropy of the title compound was also performed at HF/6‐311G(d,p) and B3LYP/6‐311G(d,p) levels of theory. The isotropic chemical shift computed by ¹H, ¹³C NMR analyses also shows good agreement with experimental observations. The theoretical spectrograms for FT‐IR and FT‐Raman spectra of the title molecule have been constructed. Copyright © 2009 John Wiley & Sons, Ltd.     

Conformational Analysis of 4,4-Dimethylheptane

Abstract

Infrared and Raman spectra were obtained for 4,4-dimethylheptane and were interpreted with the aid of normal coordinate calculations. It was shown that this compound exists in three conformations. Force constant values transferred from dimethylpentanes resulted in an overall average difference between observed and calculated wavenumbers of 4.5 cm^?1 for the three conformers.     

Infrared Spectrum and Vibrational Analysis of Bromochloromethane

Abstract

The i,r. spectrum of CH₂BrCl between 4000 and 200 cm^?1 has been investigated in the liquid phase. All the absorptions, except few features, have been identified and more than 50 bands including fundamentals, overtone and combination bands have been assigned. Anharmonicity constants from the characterized vibrational levels have been also determined. Data from liquid phase spectra are needed to correctly interpret the rather complex vapor phase features whose investigation is in progress now.