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Geometry-optimised ab initio (STO-3G minimal basis set) calculations have been carried out for S-trans and orthogonal forms of 1,3-butadiene. The central C-C bond is shorter (1.482 Å) in the S-trans form than the orthogonal form (1.504 Å). Calculations on the orthogonal form indicate that the additional bond length decrease destabilizes the σ bond. the stabilization of the S-trans form being associated with conjugative (or π delocalization) effects. 相似文献
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Oxidative cleavage of C-Si bonds of polyhydroxylated silacyclopentanes under various conditions have led to both the desired polyols and to Peterson elimination products. Further studies on the reactivity of these silacycles, under acidic and basic conditions have been carried out, leading to unexpected results. Treatment of these silacycles under basic conditions thus provided various diols after the cleavage of Csp3-Si bonds. A mechanistic rationale has been proposed for each case. 相似文献
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Badawi HM 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(7):1445-1451
The structure and conformational stability of vinylsulfonamide CH2CHSO2NH2 were investigated by DFT-B3LYP/6-311+G** and ab initio MP2/6-311+G** calculations. From the calculations the molecule was predicted to exist predominantly in the gauche-syn (vinyl group nearly eclipses one of the SO bonds and the NH2 and the SO2 moieties eclipse each other) conformation with the possibility of low abundance of the cis-syn and the gauche-anti forms. The asymmetric potential function for the internal rotation about CS bond was determined for the molecule. The vibrational frequencies were computed at DFT-B3LYP level for the gauche-syn conformer of the molecule and its d2(C2H3SO2ND2) and d3(C2D3SO2NH2) deuterated species. Normal coordinate calculations were then carried out and the potential energy distributions were calculated for the molecule. 相似文献
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Raman and i.r. spectra of the compounds (CH3)3O+ SbCl−6 and (CH3)3NH+ SbCl−6 are reported and assigned. Normal coordinate calculations support the vibrational assignments for the cations Of C3v symmetry, and yield force constants k(CO) = 4.05 mdyn·Å−1 and k(CN) = 4.80 mdyn·Å−1 for the trimethyloxonium ion and the trimethylammonium ion, respectively. 相似文献
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Silacyclopentanes have been prepared from vinyl(homoallyl)silanes or vinyl(homopropargyl)silanes and organolithium reagents by a tandem intermolecular-intramolecular sequence involving a 5-exo cyclisation process. The unexpected stereochemical outcome of the sequence involving a 5-exo-dig cyclisation is rationalised. 相似文献
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The Raman spectra of cis-2,3-dimethyloxirane and trans-2,3-dimethyloxirane in the vapor, liquid, and polycrystalline solid phases are reported for the region between 25 and 3100 cm?1. The IR spectra of these two compounds between 80 and 4000 cm?1 in the vapor and polycrystalline solid phases are also reported. In the IR and Raman spectra of gaseous trans-2,3-dimethyloxirane a total of eight torsional transitions have been observed. In the Raman spectrum of the cis compound in the vapor phase, four torsional transitions have been observed. From these experimental data, periodic barriers to the methyl torsional motions have been calculated to be 905 ± 7 cm?1 (2.5 kcal mol?1) for the trans molecule and 617 ±5 cm?1 (1.76 kcal mol?1) for the cis molecule. Additionally, complete vibrational assignments based on band contours, depolarization values, and group frequencies are proposed for both molecules and gas-phase thermodynamic functions have been calculated. These results are compared to the corresponding quantities for some similar molecules. 相似文献
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J. Umemura 《Journal of Molecular Structure》1977,36(1):35-54
Temperature dependence of the IR spectra of crystalline propionic acid were examined in the temperature range 242–50 K. The intensities of most absorption bands increased on lowering the temperature, but some bands diminished until they disappeared at temperatures lower than about 120 K. Normal coordinate analyses indicate that the former bands are due to the stable cis dimer and the latter due to the less stable trans dimer which would be produced from the cis dimer by simultaneous proton transfer along two hydrogen bonds. 相似文献
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Anharmonicity corrections to the harmonic vibrational spectra of CHFClBr and its deuterated isotopomer were computed by means of variational and perturbational approaches. A comparison of both methods is provided. Based on CCSD(T)/aug-cc-pVTZ electronic structure calculations excellent agreement with experimental data was obtained. Absolute mean deviations are in the range of about 4 cm(-1) for the fundamental modes, while slightly larger values of about 7 cm(-1) were found for the first vibrational overtones. In addition, vibrationally averaged structural parameters are provided for both molecules. The calculations will serve as a future starting point for parity-violation effects in vibrational transitions in these chiral molecules. 相似文献
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《Journal of Inorganic and Nuclear Chemistry》1981,43(2):293-298
Raman and far-IR spectra have been obtained of crystalline ZrCl4 and ZrBr4. The observed frequencies have been interpreted on the basis of the C2h symmetry of the Bravais unit cell and have been subjected to a normal coordinate analysis. The interpretation and results are satisfactorily in accord with the X-ray structure. 相似文献
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《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1976,32(1):175-183
The i.r. spectra of gaseous and solid CH3CCl2F and CH3CHClF have been recorded from 140 to 4000 cm−1. The corresponding Raman spectra of the liquids have also been recorded and depolarization values have been measured for the CH3CCl2F molecule. Also the Raman spectrum of gaseous CH3CHClF has been recorded. All spectra have been interpreted in detail and the 18 normal vibrations of both molecules have been characterized. Hot bands of the internal torsional mode for CH3CCl2F were observed at 248(2 ← 1) and 232 cm−1 (3 ← 2) in the far-i.r. spectrum of the gas. These frequencies are in good agreement with those calculated using the 4·42 kcal/mole barrier obtained in an earlier Raman study. The internal torsional mode for CH3CHClF was observed at 261 cm−1 in the spectra of the solid and the three-fold periodic barrier was calculated to be 4·38 kcal/mole. The barriers are compared in a series of chloro, fluoro and bromo substituted ethane derivatives. 相似文献
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The structural stability of sulfamoyl halides NH(2)-SO(2)X (X is F, Cl and Br) were investigated by DFT-B3LYP/6-311+G** and ab initio MP2/6-311+G** calculations. From the calculations the molecules were predicted to exist only in the anti (XS bond is anti with respect to nitrogen lone pair) conformation with the possibility of very low abundance of the syn (SO(2) and NH(2) groups eclipse each other) form of only the fluoride. The equilibrium constant for the syn<-->anti conformational conversion of sulfamoyl fluoride was calculated to be 0.0172 that corresponds to an equilibrium mixture of about 2% syn and 98% anti at 298.15K. The vibrational frequencies were computed at DFT-B3LYP level for the stable anti conformer of the d(0) and d(2) (ND(2)-SO(2)X) deuterated species of the three molecules. Normal coordinate calculations were then carried out and the potential energy distributions were calculated for the molecules. 相似文献
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《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1981,37(12):1087-1092
Complete vibrational spectra of the gold(I) halides AuX (X = Cl, Br and I) were measured. On the basis of the crystal structures symmetry analyses for both isolated chains and unit cells of the compounds were performed. Normal coordinate calculations for the chain molecules were carried out, and the most important force constants discussed. The valence force constants fd(Au-X) decrease in the series X = Cl, Br and I (1.75 × 102, 1.63 × 102 and 1.22 × 102 N m−1, respectively) and are lower throughout than the fd values for the corresponding AuX2− anions. Correlations between valence force constants and bond lengths in both AuX and AuX2− are pointed out. 相似文献
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Conclusions The Raman spectra of liquid mesitylene and the IR spectra (4000-100 cm–1) of liquid and gaseous mesitylene were studied. An assignment of the frequencies according to the symmetry and the form of the vibrations is proposed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2265–2270, October, 1982. 相似文献
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Tayyari SF Milani-nejad F 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2000,56(14):3442-2691
The infrared and Raman spectra of acetylacetone and its deuterated analogues have been analyzed by the aid of ab initio calculations at post Hartree-Fock level and considering the spectral behavior upon deuteration. By deconvolution of the infrared spectra of acetylacetone and d6-acetylacetone at 1600 cm(-1) region a broad and strong band is found and correlated with the strong Raman lines observed for these compounds in this region. The broadness of this infrared band at room temperature and it's splitting at low temperature is attributed to free rotation of methyl group attached to carbonyl group at room temperature. Furthermore it is found that all ring modes in 1200-1600 cm(-1) region more or less are mixed with the OH in plane bending motion. 相似文献
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Billes F Mohammed-Ziegler I Mikosch H Tyihák E 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,68(3):669-679
In this article the authors deal with the experimental and theoretical interpretation of the vibrational spectra of trans-resveratrol (3,5,4'-trihydroxy-trans-stilbene) of diverse beneficial biological activity. Infrared and Raman spectra of the compound were recorded; density functional calculations were carried out resulting in the optimized geometry and several properties of the molecule. Based on the calculated force constants, a normal coordinate analysis yielded the character of the vibrational modes and the assignment of the measured spectral bands. 相似文献