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41.
Zheng C Guirgis GA Herrebout WA van der Veken BJ Wurrey CJ Durig JR 《The journal of physical chemistry. A》2006,110(29):9057-9070
Variable temperature (-55 to -150 degrees C) studies of the infrared spectra (3200-100 cm(-1)) of cyclopropylmethyl isothiocyanate, c-C(3)H(5)CH(2)NCS, dissolved in liquefied rare gases (Xe and Kr), have been carried out. The infrared spectra of the gas and solid, as well as the Raman spectrum of the liquid, have also been recorded from 3200 to 100 cm(-1). By analyzing six conformer pairs in xenon solutions, a standard enthalpy difference of 228 +/- 23 cm(-1) (2.73 +/- 0.27 kJ.mol(-1)) was obtained with the gauche-cis (the first designation indicates the orientation of the CNCS group with respect to the three-membered ring, the second designation indicates the relative orientation of the NCS group with respect to the bridging C-C bond) rotamer the more stable form, and it is also the only form present in polycrystalline solid. Given statistical weights of 2:1 for the gauche-cis and cis-trans forms (the only stable conformers predicted); the abundance of cis-trans conformer present at ambient temperature is 14 +/- 2%. The potential surface describing the conformational interchange has been analyzed, and the corresponding two-dimensional Fourier coefficients were obtained. From MP2 ab initio calculations utilizing various basis sets with diffuse functions, the gauche-cis conformer is predicted to be more stable by 159-302 cm(-1), which is consistent with the experimental results. However, without diffuse functions, the conformational energy differences are nearly zero even with large basis sets. For calculations with density functional theory by the B3LYP method, basis sets without diffuse functions also predict smaller energy differences between the conformers, although not nearly as small as the MP2 results. A complete vibrational assignment for the gauche-cis conformer is proposed, and several fundamentals for the cis-trans conformer have been identified. The structural parameters, dipole moments, conformational stability, vibrational frequencies, and infrared and Raman intensities have been predicted from ab initio calculations and compared to the experimental values when applicable; the r(0) structural parameters are also estimated. The energies for the linear CNCS moiety were calculated. These experimental and theoretical results are compared to the corresponding quantities of some similar molecules. 相似文献
42.
Thermodynamics of Chromium(VI) Anionic Species Sorption onto Surfactant-Modified Montmorillonite Clay 总被引:3,自引:0,他引:3
Batch sorption experiments performed on Cr(VI) species sorption showed a significantly enhanced removal of inorganic hexavalent chromium anionic species from aqueous solution by montmorillonite clays modified with quaternary amine, hexadecyltrimethylammonium (HDTMA) bromide. Unmodified clay had no affinity for chromium(VI) species. The sorption of Cr(VI) species has been carried out as a function of pH, contact time, adsorbate concentration (4.14x10(-5) to 8.62x10(-3) M), and temperature (5-45 degrees C). The surfactant-modified clay surface was stable when exposed to extremes in pH. The optimum pH for maximum sorption of Cr(VI) species was found to be at pH 1 and was constant between pH 2 and pH 6. The sorption data obtained was well described by DKR and Langmuir sorption isotherms. Sorption energy (E) for (i) surfactant sorption by montmorillonite clay and (ii) sorption of chromium(VI) species by surfactant modified clay have been computed from the DKR equation. Sorption energy evaluated for the sorption of both surfactant and Cr(VI) species showed that an ion-exchange mechanism was operative. The mechanism of retention appears to be replacement of counterion of the surfactant by Cr(VI) anionic species. Adsorbent capacity for the sorption of Cr(VI) species has been evaluated from the Langmuir sorption isotherm data. Thermodynamic parameters (Delta H degrees, Delta S degrees and Delta G degrees ) for surfactant sorption on montmorillonite clay and Cr(VI) sorption by modified clay have been evaluated. The specific rate constant for sorption of Cr(VI) species on modified montmorillonite was rapid during the first 10 min and equilibrium was found to be attained within 30 min. The sorption of Cr(VI) species onto modified montmorillonite clay followed first-order rate kinetics. Copyright 2000 Academic Press. 相似文献
43.
Gamil A. Guirgis Yasser E. Nashed Peter Klaeboe Valdemaras Aleksa James R. Durig 《Structural chemistry》1999,10(1):1-15
The Raman spectra (3500 to 30 cm–1) of allyltrifluorosilane, CH2CHCH2SiF3, in the liquid with quantitative depolarization ratios and solid states, and the infrared spectra (3500 to 30 cm–1) of the gas and solid have been recorded. Additionally, the mid-infrared spectra of the sample dissolved in liquified xenon as a function of temperature (–100° to –55°C) have been recorded. All of these data indicate there are two conformers, the more stable gauche rotamer and a very small amount of the cis conformer in the fluid states, but only the gauche form remains in the polycrystalline solid. The variable temperature studies of the infrared spectrum of the xenon solution indicate a relatively large enthalpy difference of 354±30 cm–1 (4.23±0.36 kJ/mol) between the conformers. The fundamental frequencies for the asymmetric (54 cm–1) and SiF3 (48 cm–1) torsions for the gauche conformer were observed in the far infrared spectrum, and from the SiF3 torsional frequency the barrier to internal rotation is calculated to have a value of 525 cm–1 (6.28 kJ/mol). A complete vibrational assignment is presented for the gauche conformer that is consistent with the predicted wavenumbers utilizing the force constants from ab initio MP2/6-31G* calculations. The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios, and vibrational wavenumbers have been obtained from RHF/6-31G* and/or MP2/6-31G* ab initio calculations. These quantities are compared to the corresponding experimental quantities when appropriate as well as with corresponding results for some similar molecules.Taken in part from the dissertation of Y. E. Nashed, which will be submitted to the Department of Chemistry in partial fulfillment of the Ph.D. degree 相似文献
44.
James R. Durig Gamil A. Guirgis J. F. Sullivan T. J. Dickson D. T. Durig 《Structural chemistry》2001,12(2):149-170
The Raman (3500–40 cm–1) and infrared (3500–70 cm–1) spectra of gaseous and solid 2-methoxypropene, CH3O(CH3)C=CH2, and the isotopomers, CD3O(CH3)C=CH2 and CH3O(CD3)C=CD2 have been recorded. In addition, the Raman spectra of the liquids have been recorded with qualitative depolarization measurements. All of these data indicate that only one conformer is present in the fluid phases at ambient temperature and this form is the cis conformer, which remains in the solid. Assignments are provided for the fundamentals of all three isotopomers for the cis conformer with Cs symmetry. The far-infrared spectra of all three isotopic species have been recorded at a resolution of 0.1 cm–1 in the gas and 1.0 cm–1 in the solid. The parameters of the potential function governing the asymmetric torsion are determined to be V3 = 1485 ± 9 cm–1 and V6 = –55 ± 4 cm–1 for the d0 compound, where only two terms were determined, since a second conformer was not evident. The barrier to internal rotation for the methyl group attached to the oxygen atom is 1370 ± 8 cm–1 and the C—CH3 barrier is 772 ± 5 cm–1. Ab initio calculations with full electron correlation have been carried out by the perturbation method to second order to obtain the equilibrium structural parameters, harmonic force constants, fundamental frequencies, infrared intensities, Raman activities, depolarization values, and conformational stability. The predicted values have been compared to the experimental values where appropriate. 相似文献
45.
J.R. Durig G.A. Guirgis W.E. Bucy D.A.C. Compton V.F. Kalasinsky 《Journal of Molecular Structure》1978,49(2):323-331
The Raman spectrum of gaseous cyclobutanol has been recorded and the far infrared spectrum of the gas has been obtained at a resolution of 0.5 cm?1. At least six Q-branches arising from the low frequency ring-puckering motion have been observed and assigned on the basis of a potential of the form V(X) = (6.32 ± 0.21) × 105X4?(4.18 ± 0.04) × 104X2+ (8.81 ± 1.20) × 103X3 with a reduced mass of 170 amu. An energy difference between the equatorial and axial forms was found to be 50–150 cm?1 with the equatorial being more stable and a barrier of 700–900 cm?1 was found for the interconversion. Three O-H stretching modes were observed in the Raman spectrum. It is concluded that the O-H moiety has both the gauche and trans conformations present in the equatorial form but only the gauche conformer is present in the axial form of the ring. Three O-H torsional modes were observed at 244 (trans conformer), 226.5 and 181.5 cm?1 (gauche conformer) for the equatorial form and one O-H torsion at 237.5 cm?1 (gauche conformer) for the axial form. The potential function governing the O-H torsional motion for the equatorial form was found to be V1 = 280 ± 7 cm?1 (800 cal mole?1) and V3 = 425 ± 3 cm? (121.5 cal mole?1) with the trans conformer being more stable than the gauche by approximately 206 cm?1 (589 cal mole?). The barriers to trans-gauche and gauche-gauche interconversion have essentially the same values, 500 cm?1 (1430 cal mole?1). 相似文献
46.
Mohamed Tarek A. Guirgis Gamil A. Nashed Yasser E. Durig James R. 《Structural chemistry》1998,9(4):255-264
The infrared (3200 to 400 cm–1) and Raman (3200 to 20 cm–1) spectra of gaseous and solid ethylsilane, CH3CH2SiH3, have been recorded. Additionally, the Raman spectrum of the liquid has been obtained with quantitative depolarization values. The SiH3 torsional mode has been observed as sum and difference bands with the silicon-hydrogen stretching vibration. Utilizing the torsional fundamental frequency of 132 cm–1 the threefold periodic barrier of 590 cm–1 (7.06 kJ/mol) has been obtained. Utilizing the frequencies of the silicon-hydrogen stretches, Si-H bond distances of 1.485 and 1.484 Å have been obtained for the bonds gauche and trans to the methyl group, respectively. Using previously reported rotational constants from seven different isotopomers, the r
0 parameters have been calculated and are compared to the corresponding r
s parameters. A complete vibrational assignment is proposed that is consistent with the predicted frequencies utilizing the force constants from ab initio MP2/6-31G(d) calculations. Both the infrared intensities as well as the Raman activities and depolarization values have been obtained from the ab initio calculations. Complete equilibrium geometries have been determined by ab initio calculations employing the 6-31G(d), 6-311 + G(d,p), and 6-311+G(2d,2p) basis sets at levels of restricted Hartree–Fock (RHF) and/or Moller–Plesset (MP) to second order. The results are discussed and the theoretical values are compared to the experimental values when appropriate. 相似文献
47.
James R. Durig Joshua J. Klaassen Arindam Ganguly Todor K. Gounev Gamil A. Guirgis Wei Lin 《Structural chemistry》2008,19(6):935-948
Variable temperature (?55 to ?100 °C) studies of the infrared spectra (4,000–400 cm?1) of chlorocyclobutane, c-C4H7Cl, dissolved in liquid xenon have been carried out. The infrared spectrum (4,000–100 cm–1) of the gas has also been recorded. For this puckered ring molecule the enthalpy difference between the more stable equatorial conformer and the axial form, has been determined to be 361 ± 17 cm?1 (4.32 ± 0.20 kJ/mol). This stability order is consistent with that predicted by ab initio calculations but the ?H is much lower than the average energy value of 646 ± 73 cm?1 obtained from the MP2 ab initio calculations or 611 ± 28 cm?1 from the B3LYP density functional theory calculations. The percentage of the axial conformer present at ambient temperature is estimated to be 15 ± 1%. By utilizing previously reported microwave rotational constants for both conformers combined with ab initio MP2(full)/6–311+G(d,p) predicted structural values, adjusted r 0 parameters have been obtained. The determined heavy atom structural parameters for the equatorial conformer are: the distances C–Cl = 1.783(5), C1–C4 = 1.539(3), C4–C6 = 1.558(3) Å, and angles ∠C6C4C1 = 86.9(5), ∠C4C1C5 = 89.7(5)°, and for the axial conformer are: the distances C–Cl = 1.803(5), C1–C4 = 1.547(3), C4–C6 = 1.557(3) Å, and angles ∠C6C4C1 = 86.3(5), ∠C4C1C5 = 88.9(5) and the puckering angles for the equatorial and axial conformers are 30.7(5)° and 22.3(5)°, respectively. The conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios and vibrational frequencies have been obtained for both conformers from MP2(full)/6-31G(d) ab initio calculations and compared to experimental values where available. The results are discussed and compared to the corresponding properties of some similar molecules. 相似文献
48.
Variable temperature (–55 to –150°C) studies of the infrared spectra (3500 to 400 cm–1) of 1-fluoropropane, CH3CH2CH2F, dissolved in liquid krypton and xenon have been recorded. Utilizing three conformer pairs in the krypton solution and four conformer pairs in the xenon solution, enthalpy differences of 104±6 cm–1 (1.24±0.07 kJ/mol) and 99±5 cm–1 (1.16±0.06 kJ/mol) were obtained from the krypton and xenon solutions, respectively, with the gauche form the more stable conformer. From these data it is estimated that 24% of the trans forms is present at ambient temperature. The conformational stabilities, harmonic force constants, fundamental frequencies, infrared intensities and Raman activities have been obtained from RHF/6-31G(d) and/or MP2/6-31G(d) ab initio calculations and these quantities have been compared to the experimental values when appropriate. The optimized geometries have also been obtained with several different ab initio basis sets up to MP2/6-311+G(2d,2p). The r0 structural parameters have been obtained by combining the ab initio data with the previously reported rotational constants for both conformers. The results are compared to the corresponding results for some similar molecules. 相似文献
49.
Gamil A. Guirgis Todor K. Gounev Pengqian Zhen James R. Durig 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1999,55(14):2753
The infrared (3500–40 cm−1) spectra of gaseous and solid 1-fluoro-1-methylsilacyclobutane, c-C3H6SiF(CH3), have been recorded. Additionally, the Raman spectrum (3500–30 cm−1) of the liquid has been recorded and quantitative depolarization values have been obtained. Both the axial and equatorial (with respect to the methyl group) conformers have been identified in the fluid phases. Variable temperature (−55–−100°C) studies of the infrared spectra of the sample dissolved in liquid xenon have been carried out. From these data, the enthalpy difference has been determined to be 267±10 cm−1 (3.19±0.12 kJ mol−1), with the axial conformer being the more stable form and the only conformer remaining in the polycrystalline solid. A complete vibrational assignment is proposed for the axial conformer and many of the fundamentals for the equatorial conformer have also been identified. The vibrational assignments are supported by normal coordinate calculations utilizing ab initio force constants. Complete equilibrium geometries have been determined for both rotamers by ab initio calculations employing the 6-31G* and 6-311++G** basis sets at the levels of restricted Hartree–Fock (RHF) and/or Moller–Plesset (MP) to second order. The results are discussed and compared to those obtained for some similar molecules. 相似文献
50.
Guirgis Gamil A. Nashed Yasser E. Gounev Todor K. Durig James R. 《Structural chemistry》1998,9(4):265-277
The Raman spectra (3500 to 30 cm–1) of allylsilane, CH2CHCH2SiH3, in the liquid with quantitative depolarization ratios and solid states and the infrared spectra (3500 to 30 cm–1) of the gas and solid have been recorded. Similar data have also been recorded for the Si-d3 isotopomer. Additionally, the mid-infrared spectra of the normal sample dissolved in liquified xenon as a function of temperature (–100 to –50°C) have been recorded. All these data indicate there is a single conformer, the gauche rotamer, in all three physical states. Utilizing the Si-H stretching frequencies from the infrared spectrum of the gaseous CH2CHCH2SiD2H isotopomer, the three Si-H bond distances (r
0) are calculated to be 1.484 Å for the gauche conformer. The other r
0 parameters are estimated from the previously reported rotational constants. The fundamental frequencies for the asymmetric (78 cm–1) and SiH3 (137 cm–1) torsions were obtained from sum and difference bands with the SiH3 stretches. From the SiH3 torsional frequency the barrier to internal rotation is calculated to have a value of 731 cm–1 (8.74 kJ/mol). The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios, and vibrational frequencies have been obtained from RHF/6-31G* and/or MP2/6-31G* ab initio calculations. These quantities are compared to the corresponding experimental quantities when appropriate as well as with some corresponding results for some similar molecules. 相似文献