Far IR and Raman vibrational spectra of nitramines

Vibrational spectra of several nitramines in the long-wave region (50–450 cm⁻¹) were studied. The frequencies of intra- and intermolecular vibrations were separated and a tentative assignment of the frequencies of self-associative complexes was performed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2241–2244, November, 1998.     

Molecular structure and vibrational spectra analysis of diethylsilanediol by IR and Raman spectroscopies and DFT calculations

A thorough theoretical analysis (DFT/B3LYP) of the potential energy surface of diethylsilanediol (DESD) allowed finding ten stable conformations of the molecule, differing on the relative arrangement of both ethyl and hydroxyl groups. The Boltzmann??s population analysis allowed establishing their stability order that was justified in terms of the anomeric effect analyzed by means of the Natural Bond Orbitals methodology. Besides, DESD was synthesized and characterized using FT-IR and Raman spectroscopies data, firstly reported in this work, combined with DFT calculations (B3LYP/aug-ccpVTZ). Finally some of the main structural and vibrational features of this and other closely related alkylsilanediols, i. e. DMSD and EMSD, have been put together in order to establish some trends that can allow a better understanding of the chemistry of these compounds.     

IR and Raman spectra,density functional computations of vibrational spectrum,molecular geometry,atomic charges,and some molecular properties of 3‐aminobenzonitrile molecule

Geometry, vibrational wavenumbers, and several thermodynamic parameters have been calculated using ab initio quantum chemical methods for the 3‐aminobenzonitrile molecule for the first time. The results were compared with experimental values. With the help of specific scaling procedures, the observed vibrational wavenumbers were analyzed and assigned to different normal modes of the molecule. In general, the error obtained was very low. Using potential energy distribution (PED), the contributions of the different modes to each wavenumber were determined. Other general conclusions were also deduced. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Density functional theory study on molecular structure and vibrational IR spectra of isocytosine

Density functional theory with the combined Becke3-LYP exchange-correlation energy functional [DFT(B3-LYP) method] using the 6-31G(d, p) basis set is applied to predict molecular parameters (geometries, rotational constants, dipole moments) and vibrational IR spectra (harmonic wavenumbers, absolute intensities) of six tautomers of the isocytosine molecule. The results are compared with the corresponding data calculated at the conventional ab initio Hartree-Fock (HF) level using the same basis set and with available experimental data. Calculations show that (a) three amino tautomers are slightly nonplanar species with, evidently, a distorted amino group, (b) the DFT (B3-LYP)/6-31G(d, p) method predicts better molecular parameters, than do the HF calculations, and (c) the DFT(B3-LYP)-calculated vibrational IR spectra of isocytosine agree well with the available recorded IR spectra, and they show marked improvement over the IR spectra predicted at the HF/6-31G(d, p) level. Tautomeric stabilities of isocytosine are discussed on the basis of computed electronic energies by the DFT(B3-LYP) and ab initio approaches [including the MP2 and MP4(SDQ) calculations of electronic energies] and predicted zero-point vibrational energies by DFT(B3-LYP) and HF methods. This relative energies at 0 K of the tautomeric forms of isocytosine predicted by both conventional ab initio and DFT(B3-LYP) methods correlate well with the experimental data, showing the predominance of the aminohydroxy tautomer of isocytosine for an isolated molecule. © 1997 John Wiley & Sons, Inc.     

Effect of ligand radicals on vibrational IR, Raman and vibronic spectra of europium beta-diketonates

Vibrational IR, Raman spectra and vibronic sidebands of Eu(3+) electronic transitions of europium tris-beta-diketonates Eu(beta)(3).Ph (beta-dipyvaloylmethane (DPM), acetylacetone (AA), benzoylacetone (BA), thenoyltrifluoroacetone (TTFA) and other beta-diketones; Ph-methyl-, phenyl-, and nitro-derivatives of 1,10-phenanthroline (Phen)) as well as Eu(beta)(3).Bpy and Eu(beta)(3).D-Bpy (Bpy- and D-Bpy-H- and D-2,2'-bipyridine) were studied. Effect of ligand radical properties on spectra and manifestation of the reciprocal influence of non-equivalent ligands in spectra are discussed. Dependence of the spectra on electronic density distribution in both ligands as well as on the strength of M-O and M-N bonds at the variation of radicals of one of the ligands, beta or Ph, was examined. Shape of vibronic sidebands was analysed. Behaviour of bands in the middle and far regions of IR spectra of the series Eu(beta)(3).Phen and Eu(TTFA)(3).Ph was investigated. Increase of the polarising influence of Eu(3+) ions on Phen and Bpy molecules and strengthening the Eu-N bonds in TTFA compounds in comparison with DPM compounds were disclosed from the Raman spectra of Eu(beta)(3).Phen and Eu(beta)(3).Bpy, that is in accordance with properties of beta-diketone radicals. Conclusion about weaker Eu-N bonds in europium beta-diketonates with heterocyclic diimines in comparison with corresponding nitrates was derived from the spectra. Spectral data concerning the relative strength of Eu-ligand bonds are in agreement with available X-ray data.     

The low frequency IR and Raman spectra of some complexes of dithiooxamide with cadmium halides

summary The low frequency IR and Raman spectra of Cd(DH ₄)X ₂ (X=Cl, Br;DH=dithiooxamide) have been discussed. On the basis of the cadmium isotope and H-D shift as well as chlorine-bromine substitution a band assignment in the region 500–33 cm^–1 has been made. A polymeric structure of Cd(DH ₄)X ₂ involving both dithiooxamide and halogen bridges with D_4h symmetry of the cadmium environment is assumed.

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Die niederfrequenten IR- und Raman-Spektren einiger Komplexe von Dithiooxamid mit Cadmiumhalogeniden

Zusammenfassung Die IR- und Raman-Spektren von Cd(DH ₄)X ₂ (X=Cl, Br;DH=Dithiooxamid) werden im Bereich niedriger Frequenzen diskutiert. Basierend auf Cadmiumisotopen- und H-D-Verschiebungen mit zusätzlicher Cl-Br-Substitution werden die Banden im Bereich von 500–33 cm^–1 zugeordnet. Es wird eine polymere Struktur von Cd(DH ₄)X ₂ unter Anteilnahme sowohl von Dithioxamid- als auch Halogenbrücken mit einer D_4h-Symmetrie im Bereich des Cadmiumzentralions angenommen.

     

Experimental IR and Raman spectra and quantum chemical studies of molecular structures, conformers and vibrational characteristics of nicotinic acid and its N-oxide

FTIR and Raman spectra of nicotinic acid and its N-oxide have been recorded and analyzed. The stabilities, optimized molecular geometries, APT charges and vibrational characteristics for the two possible conformers of nicotinic acid and its N-oxide have been computed using DFT method. The E (trans) conformers of both the molecules are found to be more stable and less polar than their respective Z (cis) conformers. Due to addition of an O atom at the N1 site in nicotinic acid the magnitudes of atomic charges on all the H atomic sites of the nicotinic acid N-oxide molecule are found to increase. Most of the vibrational frequencies have nearly the same magnitude for the two conformers of both the molecules. However, significant changes are noticed in their IR intensities, Raman activities and depolarization ratios of the Raman bands. The calculated frequencies have been correlated with the experimental frequencies.     

Electronic and vibrational resonance Raman spectra of octamethyluranocene

The Raman spectrum of bis(tetramethylcyclo-octatetraene)uranium (U(TMCOT)₂), excited in resonance with its visible charge-transfer transitions shows an anomalously polarized electronic band at 473 cm^?1, twice as broad as the analogous band of uranocene, at 466 cm^?1. The broadening is attributed to crystal-field splitting associated with the lowered symmetry introduced by the methyl group, and/or a distribution of rotamer populations. Totally symmetric vibrational modes are observed at 879, 750, 580, 513 and 95 cm^?1; possible assignments are discussed.     

Experimental IR and Raman spectra and quantum chemical studies of molecular structures, conformers and vibrational characteristics of L-ascorbic acid and its anion and cation

IR and spectra of the L-ascorbic acid (L-AA) also known as vitamin C have been recorded in the region 4000-50 cm(-1). In order to make vibrational assignments of the observed IR and Raman bands computations were carried out by employing the RHF and DFT methods to calculate the molecular geometries and harmonic vibrational frequencies along with other related parameters for the neutral L-AA and its singly charged anionic (L-AA(-)) and cationic (L-AA(+)) species. Significant changes have been found for different characteristics of a number of vibrational modes. The four ν(O-H) modes of the L-AA molecule are found in the order ν(O(9)-H(10))>ν(O(19)-H(20))>ν(O(7)-H(8))>ν(O(14)-H(15)) which could be due to complexity of hydrogen bonding in the lactone ring and the side chain. The CO stretching wavenumber (ν(46)) decreases by 151 cm(-1) in going from the neutral to the anionic species whereas it increases by 151 cm(-1) in going from the anionic to the cationic species. The anionic radicals have less kinetic stabilities and high chemical reactivity as compared to the neutral molecule. It is found that the cationic radical of L-AA is kinetically least stable and chemically most reactive as compared to its neutral and anionic species.     

Structure and vibrational spectra of some 8-oxa[5]helicenes

A systematic study has been conducted on the geometrical and electronic structure, heliomeric conformations of a series of 8-oxa[5]helicenes based on density functional theory (DFT) computations. A complete vibrational analysis has also been attempted for one of the 8-oxa[5]helicenes (molecule 5) on the basis of experimental infrared spectra in the far and mid infrared regions (60-3100 cm(-1)) and density functional theory computations using B3LYP/6-31G** method characteristic bands of the molecule identified. The approximate mean plane angle between the terminal rings A and E in the presently studied molecules are found to have values between 48.64° and 59.46°. This angle is much larger than the corresponding angle between the terminal rings in benzo[c]phenanthrene (～27°) and partially reduced benzo[c]phenanthrene (34.6-46.0°) and indicates that the presence of oxygen-containing six-membered ring provides a greater helicity to the molecules. Detailed quantum chemical study on molecule 4 shows the existence of two enantiomeric forms M- and P- of almost equal energy separated by a potential barrier of 15.55 kcal/mol. It is expected that similar 8-oxa[5]helicines (molecules 3, 5 and 6) may also exist in two enantiomeric forms.     

Electronic and vibrational spectra of some dihydroxypyrimidines

In the present paper, we report the analysis and assignment of the electronic absorption spectra of 4(6) methyl-, 5,6-dimethyl- and 5-bromouracil in the light of their ketonic structure and the electronic and vibrational spectra of 4,6-dihydroxypyrimidine in the light of its keto enolic structure.     

Far IR and Raman spectra of some gaseous titanium,zirconium and hafnium cyclopentadienyl chlorides

The far IR and Raman spectra of gaseous (C₅H₅)TiCl₃ and (C₅H₅)₂MCl₂ species (M = Ti, Zr and Hf) are reported. The results are compared to the previous vibrational analysis of the corresponding species in the solid and matrix isolated phases. The assignment of the metal skeletal vibrations is reexamined in further detail on the basis of the new spectroscopic measurements. The torsional frequencies and the related potential barriers are investigated.     

The vibrational Raman spectra of selenium trioxide ag

The vibrational Raman spectra of selenium trioxide have been observed in the solid and vapour phases for the same sample. The spectrum of the vapour phase, which essentially arises from the monomeric species SeO₃, has provided for the first time values of the Raman-active ν₁, ν₃ and ν₄ wavenumbers of SeO₃. The spectrum of the solid phase represents an improvement on previous work and has enabled a partial assignment of the tetrameric species (SeO₃)₄ to be made.     

Coupled-cluster calculations of vibrational Raman optical activity spectra

We present the first calculations of Raman optical activity spectra at the coupled-cluster level of theory. Calculations are presented for (S)-methyloxirane and compared to recent experimental gas-phase measurements as well as the results obtained at the Hartree-Fock and density functional level of theory using the popular B3LYP functional. For the experimentally relevant frequency region of 400-1600 cm(-1), the Hartree-Fock, B3LYP and coupled-cluster spectra are very similar when the same force field is used, and the results also agree well with experiment. For high-frequency vibrational modes, differences in the ROA difference parameters are observed and are analyzed. The new coupled-cluster ROA code will allow for critical benchmarking of the accuracy of modern exchange-correlation functionals in the calculation of ROA spectra.     

Raman spectra of some terpenes

Summary Investigation of Raman spectra indicates increase in the interaction between the double bonds as we pass from sylvestrene and isosylvestrene to sylveterpinolene and indicates that the character of the interaction in the last compound is more complex than in 1,3-butadiene and other similar conjugated systems.     

IR and polarized Raman spectra of strontium tartrate trihydrate

The IR and polarized Raman spectra of SrC₄H₄O₆ · 3H₂O have been recorded and analysed. The factor group analysis of the divalent tartrate ion has been carried out on the basis of C₂ symmetry. As the ion possesses lower symmetry in the crystal, splittings have been observed for the different vibrational modes. Separate bands in the bending region of water suggest the existence of three crystallographically different water molecules in the crystal, which is confirmed by deuterium substitution.     

IR, Raman and SERS spectra of disodium terephthalate

The IR and Raman spectra of disodium terephthalate were recorded and analysed. Surface enhanced Raman scattering (SERS) spectrum was recorded in silver colloid. The vibrational wavenumber of the compound have been computed using the Hartree-Fock/6-31G* basis and compared with the experimental values. SERS studies suggest a flat orientation of the molecule at the metal surface.     

IR, Raman and SERS spectra of 2-phenoxymethylbenzothiazole

The FT-IR and FT-Raman spectra of 2-phenoxymethylbenzothiazole 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 and compared with the experimental values. The appearance of the Ag–O stretching mode at 237 cm⁻¹ in the SERS spectrum along with theoretically calculated atomic charge density, leads us to suggest that the molecule is adsorbed through the oxygen atom with the molecular plane tilted on the colloidal silver surface. The direction of charge transfer contribution to SERS has been discussed from the frontier orbital theory.