Vibrational spectra of thioanhydrides I. Succinic thioanhydride (original) (raw)
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The ir absorption of gaseous HNSO, DNSO and H15NS0 is recorded in the range 300-4100 cm-' at medium resolution. Besides the fundamental vibrations, overtones and combination bands are measured and assigned. From these data, combined with the ir absorptions of four more isotopic species of thionylimide, and with the centrifugal distortion constants of HNSO and DNSO. a harmonic force field, with 11 constants was derived.
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Spectroscopic and theoretical study of vibrational spectra of hydrogen-bonded 2,4-dithiouracil
Journal of Molecular Structure, 2000
Theoretical simulation of the bandshape and ®ne structure of the n s stretching band is presented for 2-pyridone-H and 2-pyridone-D, taking into account an adiabatic coupling between high-frequency N±H(D) stretching and low-frequency intermolecular N´´´O stretching modes, Davydov interactions and linear and quadratic distortions of the potential energies for the low-frequency vibrations in the excited state of the N±H(D) stretching vibrations. In order to determine the low-frequency vibrations, the experimental spectra of the polycrystalline 2-pyridone in the far infrared and the low-frequency Raman range have been recorded. The experimental frequencies in the low-frequency region are compared with the results of the HF/6-31G pp and Becke3LYP/6-31G pp calculations carried out for the 2-pyridone dimer.
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European Journal of …, 2010
The FT-IR and FT-Raman spectra of 1,3-diphenyl thiourea were recorded and analyzed. The vibrational wavenumbers were examined theoretically with the aid of the Gaussian03 package of programs using the HF/6-311++G(d,p) and B3LYP/6-311++G(d,p) levels of theory. The data obtained from vibrational wavenumber calculations are used to assign vibrational bands obtained in IR and Raman spectroscopy of the studied molecule. The first hyperpolarizabililty, infrared intensities and Raman activities are reported. The calculated first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive object for future studies of non-linear optics. The geometrical parameters of the title compound are in agreement with the values of similar structures. The changes in the C-N bond lengths suggest an extended π-electron delocalization over the thiourea moiety which is responsible for the non-linearity of the molecule.
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Raman intensities are calculated for the torsional vibrations of CH 3 CH,CI, CH 3 CH,Br, CH 3 CH,I, CH 3 CHCI" and CH 3 CHBr, using an anisotropic atom-point dipole interaction model to calculate the elements of the molecular polarizability tensor. The calculated relative intensities for the members of the Llv = 2 torsional overtone progression of each of the ethyl halides are in good agreement with experiment. It is predicted that electrically anharmonic terms contribute substantially to the Raman intensities of these transitions. The Llv = I torsional transitions of the five molecules are predicted to be 20-30 times more intense than the overtones (although these transitions are not observed because of broadband contours and interference from other vibrational modes). Electrically anharmonic terms in the polarizability expansions also contribute substantially to the intensity of the fundamentals.
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Journal of Molecular Spectroscopy, 1981
The structures, dipole moments, force fields, and a~~monic frequencies for the planar co~ormation of formamide and thioformamide were calculated using the unscaled 4-31G basis set, augmented with a full set of d functions on the sulfur, and full geometry optimization. Extensive comparison of the geometries are made, especially the C=O and C=S bond lengths, with both the experimental values for the amides and values calculated in previous studies on the acids and other carbonyl compounds. Comparison of the dipole moments calculated using the optimized and experimental geometries with the experimental values suggest there is some in~onsistancy in the experimental geometry for thioformamide. Quadratic, cubic, and quartic force constants are calculated for both amides, and hence the tindamental vibration frequencies. Critical comparisons are made with the assignments based on experimental observations. Differences in the bond lengths and stretching force constants for the two N-H bonds are shown to be consistent with a hydrogen-bonding type of interaction between the proximal N-H and C=O and C=S groups, like that in the acids.
High Overtones of the C−H Stretching Vibrations in Anisole and Thioanisole
The Journal of Physical Chemistry A, 2002
The high overtone C-H stretching vibrations of anisole and thioanisole have been measured in liquid phases by using optical absorption and optoacoustic spectroscopy. The local mode model satisfactorily describes the experimental data and provides anharmonicities and force constants. The data obtained by the DFT calculations allow a complete assignment of all the observed bands in the vibrational spectra of the two molecules. The comparative analysis of the overtone spectra and of the DFT results confirms the occurrence of the methyl C-H symmetric stretching at low wavenumber (∼2836 cm -1 ) in anisole as due to a strong anharmonic coupling, deriving from a Fermi resonance with the first overtone of the methyl symmetric deformation mode. This effect is typical of the methoxy group, because it does not occur in thioanisole as well as in toluene. The present investigation demonstrates the existence of a strong effect of electron conjugation of OCH 3 toward the aromatic system, in comparison with the SCH 3 group, as evidenced also by the study of the rotational barriers and the proton magnetic resonance data.