Theoretical studies of molecular structure and vibrational spectra of O-ethyl benzoylthiocarbamate

O-Ethyl benzoylthiocarbamate has been synthesized and characterized by elemental analysis and FT-IR. The crystal structure was determined by X-ray diffraction analysis. Title compound crystallizes in the orthorhombic space group Pna2(1), with Z=4. Unit cell parameters a=9.941(3)A, b=9.352(3)A, c=10.962(3)A and V=1019.1(5)A(3). The molecular geometry and vibrational frequencies of O-ethyl benzoylthiocarbamate in the ground state has been calculated using the Hartree-Fock and density functional using Becke's three-parameter hybrid method with the Lee, Yang, and Parr correlation functional (B3LYP) methods with 3-21G and 6-31G(d) basis sets. The computational frequencies are in good agreement with the observed results. Comparison of the observed fundamental vibrational frequencies of O-ethyl benzoylthiocarbamate and calculated results by density functional B3LYP and Hartree-Fock methods indicate that B3LYP is superior to the scaled Hartree-Fock approach for molecular vibrational problems.     

Infrared and Raman spectra of N-n-alkylthioureas

The i.r. and Raman spectra of solid alkyl thioureas H₂NCSNH(CH₂)nCH₃ (n = 0–15), TUR′, and their urea analogue H₂NCONH(CH₂)nCH₃ (n = 0–9), UR′, are presented. The vibrational properties of N-monosubstituted TUR′and UR′are studied on the basis of the spectral comparison between the members of the series and compared with the properties of N,N′-di-substituted MTUR′ and MUR′, correspondingly. Some features of the methylene ν₄ and ν₇ band progressions were found to shift from the corresponding features of solid n-alkanes by vibrational coupling. The observed wavenumber of the longitudinal accordion-like skeletal motion (LAM-1) of TUR′ was found to correspond to that of the n-alkane with the same number of carbon atoms as TUR′ has skeletal atoms.     

Infrared and Raman spectra of pyromellitic dithioanhydride

The i.r. spectrum of pyromellitic dithioanhydride has been measured from 4000 to 200 cm⁻¹; polarized i.r. spectra of single crystals have been also obtained. The Raman spectra of polycrystalline samples and solutions have been recorded and polarization of many lines has been determined. A detailed assignment of most of the fundamentals has been proposed on the basis of i.r. dichroism of the single crystals, Raman spectra and analogies with the spectra of related molecules.     

Infrared and Raman spectra of 2,4-dimethylaniline

The infrared spectra of 2,4 dimethylaniline have been recorded in the region 3600-100 cm⁻¹. The Raman spectra with polarization measurements have been recorded and investigated for the first time in the region 3500-100 cm⁻¹. New frequency assignments have been proposed assuming the molecule to possess an approximateC ₂ symmetry. Fifty normal modes of the molecule, out of a possible fifty four modes, have actually been observed and assigned including twenty seven hitherto unreported frequencies. The observed spectral changes give evidence of the presence of an intermolecular hydrogen bonding of an N−H...N type, and suggest a solid-solid phase transition between 223 and 123 K in the molecule.     

Infrared and Raman spectra of phthalimide and isatin

The i.r. spectra of phthalimide and isatin have been measured from 4000 to 200 cm⁻¹; polarized i.r. spectra of oriented single crystals have been also obtained. The Raman spectra of polycrystalline samples and solutions have been measured and polarization of many lines has been determined. A detailed assignment of most of the observed frequencies has been proposed on the basis of dichroism of the single crystals, Raman spectra and analogies with the spectra of related molecules.     

Infrared and Raman spectra of cytosine and cytidinium salts

Studies of the infrared and Raman spectra of cytidinium salts are presented. They are supplemented by the measurements of the infrared spectra of the c     

Infrared and Raman spectra of quinolinic thioanhydride and N-methyl-quinolinimide

The i.r. spectra of quinolinic thioanhydride and N-methyl-quinolinimide have been obtained from 4000 to 200 cm⁻¹; polarized spectra of oriented samples have been also obtained. The Raman spectra of polycrystalline samples and solutions have been measured and polarization of many lines has been determined. A detailed assignment of most of the observed frequencies has been proposed based upon dichroism of the oriented samples, Raman polarization data and analogies with the spectra of related molecules.     

Infrared and Raman spectra of octa(hydridosilasesquioxanes)

We report the NIR FT-Raman spectrum of H₈Si₈O₁₂ and the fundamental IR modes of D₈Si₈O₁₂. The fundamental modes are assigned according to a normal coordinate analysis and in terms of internal vibrations.     

Theoretical study of the local structure and Raman spectra of CaO-SiO2 binary melts

A procedure for the Raman spectra calculation of vitreous and molten silicates was presented in this paper. It includes molecular dynamics MD simulation for the generation of equilibrium configurations, Wilson's GF matrix method for the calculations of eigenfrequencies and corresponding vectors, electro-optical parameters method (EOPM) for the Raman intensity calculations, and the bond polarizability model (BPM) for the determination of polarizability and polarizability derivative. One of the most important characteristics of this procedure is the achievement of the partial Raman spectra of five tetrahedral units, as well as the total spectral envelope. In this paper, the calculation was carried out for the vitreous and molten calcium silicates with different compositions and at various temperatures. It is worthwhile to note that the calculation is based on statistical configurations distribution in the space and so it is not needed to artificially adjust the full width at half maximum (FWHM) of spectra. It was also tested through the good agreement of the calculated spectra with the experimental, including some regularity of spectral properties. According to the calculation, the symmetrical stretching of whole tetrahedral units, to which the stretching of Si-O(nb) bond gives the main contribution to intensity, is proven to be the dominance in the high-frequency range (800-1200 cm(-1)) and the symmetrical bending of Si-O(b)-Si, to which the stretching of Si-O(b) bond exhibits the main contribution, is the dominance in the medium-frequency range (400-700 cm(-1)). As the first theoretical results, the Raman scattering coefficient of each Q(i) was found little change along with the variation of composition and temperature.     

Infrared and Raman spectra of 8-azaguanine and 8-azaadenine

The IR and Raman spectra of 8-azaguanine and 8-azaadenine have been studied. The spectra of 8AG have been critically examined and compared with those of guanine and 9-methylguanine. Similarly, the spectra of 8-azaadenine have been examined and compared with those of adenine and 9-methyladenine. It has been possible to refute or accept the assignments for certain frequencies proposed earlier in the parent molecules by other workers, and thus almost unambiguous assignments for several frequencies in guanine and adenine as well as in 8AG and 8AA have been obtained. Several frequencies have been explained as combinations involving a 130 cm⁻¹ vibration which has been assigned to the ring-folding mode. It is found that not as many combination bands involving this mode occur in 8AA as those in 8AG. These observations indicate that guanine and 8AG are geometrically more flexible than adenine and 8AA.     

Infrared and Raman spectra and normal coordinate analysis of disilylchloride

Disilylchloride has been synthesized by chlorination of disilane with boron trichloride. FTIR spectra have been obtained of the vapour phase and Raman spectra of the liquid phase of this molecule. The spectra are fully assigned for the first time. A normal coordinate analysis is carried out and the refined force constants are compared to previous works on disilane, disilyliodide and silylchloride. The height of the potential energy barrier to internal rotation in disilylchloride is also evaluated.     

Infrared and Raman spectra of alkali metal salts of TCNQ

The infrared and Raman spectra of the series of alkali metal salts of the monoanion radical of tetracyanoquinodimethane MTCNQ (M = Li, Na and K) are observed and analysed both in the low-frequency lattice vibration region and in the intramolecular vibration region. The vibrational assignments are made, by comparing the spectra of MTCNQ with one another and investigating the difference between the powder and solution spectra and the temperature dependence of the spectra. The monomer—dimer phase transition in NaTCNQ and KTCNQ of the columnar stacking of TCNQ⁻ does not cause a marked change in the low-frequency spectra due to the lattice vibrations. The vibronically activated bands of the totally symmetric modes of the TCNQ⁻ anion are observed in the infrared spectra, which are associated with the charge-transfer intermolecular interaction. A lattice dynamical analysis for the optically active crystal vibrations of NaTCNQ and KTCNQ is performed, and the result of this calculation also verifies the vibrational assignments of the low-frequency infrared and Raman bands attributed experimentally to the translational and rotational lattice modes.     

Infrared,matrix i.r. and Raman spectra of hexachloro-2-propanol

The i.r. spectra of the alcohol CCl₃CHOHCCl₃ have been recorded in the gaseous and solid phases, in argon, krypton, nitrogen and carbon monoxide matrices and in various solutions. Raman spectra of the solid alcohol and its solutions were also recorded. Assignments of the vibration bands are made on the basis of an approximate normal coordinate calculation. The alcohol exhibits two conformers in the vapour phase and in solutions; the relative stabilities of these conformers are discussed. When the temperature is varied, a reversible interconversion between two species of the alcohol occurs in nitrogen matrices. The self-association tendency of the alcohol is very weak.     

Infrared and Raman spectra of crystalline para-bromoaniline at low temperatures

The polarization characteristics of the i.r. absorption bands of oriented p-bromoaniline crystal films have been studied at low temperatures. Raman spectra of this compound in solution and in the polycrystalline state have been recorded as an aid to the vibrational assignment of the crystal bands. The vibrational spectra are interpreted to deduce the crystal factor group (D_2h) and the molecular site symmetry (C_s). The observed factor group splittings and dichroic ratios suggest the crystal unit cell of p-bromoaniline to be isostructural with that of p-chloroaniline.     

Infrared and Raman spectra and normal coordinate calculations for methylisothiocyanate

The infrared spectra (3200-50 cm^?1) of gaseous and solid CH₃NCS and CD₃NCS and the Raman spectra (3200-10 cm^?1) of the liquids and solids have been recorded. The spectra have been interpreted on the basis of a “pseudo-symmetric top” with C_3v symmetry. An assignment of the fundamental vibrations in both molecules, based on their infrared band contours, depolarization values and group frequencies, is given and discussed. Particularly interesting is the low-frequency region where band maxima were observed at 152 and 80 cm^?1 for CH₃NCS and 139 and 71 cm^?1 for CD₃NCS in the infrared spectra of the gases. A normal coordinate analysis has also been carried out based on C_3v symmetry. Considerable mixing was found between the C_αN stretch and NCS symmetric stretch in both isotopic species. The other normal modes in CH₃NCS are reasonably pure but, for the CD₃NCS molecule, considerable mixing was found between the CD₃ stretches and NCS antisymmetric stretch. The proposed vibrational assignment and the results of the normal coordinate calculations are discussed and compared with the results obtained for similar molecules.     

Theoretical and experimental studies on the Raman spectra of electrosynthesized polynaphthalene

Polynaphthalene (Pnap) was electrosynthesized through the direct oxidation of naphthalene in boron trifluoride diethyl etherate and was characterized with IR and Raman spectroscopy, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectroscopy, and thermogravimetric analysis. Raman spectra of oligonaphthalene were calculated with Gaussian 98 at the B3LYP/6‐31G* level. Combining the computational and experimental results, we assigned the Raman bands of pristine Pnap. The Raman bands related to the chain‐stretching vibrations of Pnap around 1600 cm^?1 shifted to higher wave numbers as the polymerization degree increased. This phenomenon was in contrast to that of other conducting polymers bearing simple aromatic rings, such as polythiophene and polyfuran. The reason was that the condensed ring of Pnap and the steric repulsion of the interring hydrogen atoms prevented the elongation of conjugation sequences with the polymer chain length. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 241–251, 2005     

Infrared and Raman spectra of phtalic,isophtalic and terephtalic acids

The i.r. spectra of phtalic, isophtalic and terephtalic acids as KBr pellets as well as Raman spectra of microcrystalline powder have been investigated. Most vibrations have been assigned by correlation with the spectra of the previously studied phtalate, isophtalate and terephtalate ions. The COOH characteristic vibrations have been assigned as vibrations of the hydrogen-bonded centrosymmetric “dimers” COOH … HOOC, and a general assignment is proposed for combination bands in the range 3000-2500 cm⁻¹.     

Infrared and Raman spectra and thermodynamic functions of 4-methoxypyridine N-oxide

The infrared spectrum of 4-methoxypyridine N-oxide in the region 4000-30 cm⁻¹ in the solid and liquid states and the polarized laser Raman spectrum of the molecule in the liquid state have been investigated. A vibrational assignment of the observed frequencies based on the state of polarization of the Raman lines and comparison with the related molecules is presented. Ideal gas state thermodynamic functions of the molecule are calculated in the temperature range 273·15–1500° K.