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41.
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 C3v 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 C3v symmetry. Considerable mixing was found between the CαN 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. 相似文献
42.
Hassan M. Badawi Wouter A. Herrebout Chao Zheng Tarek A. Mohamed B. J. van der Veken James R. Durig 《Structural chemistry》2003,14(6):617-635
The infrared spectra (3500–400 cm–1) of krypton solutions of chlorocyclopentane, c-C5H9Cl, at variable temperatures (–101 to –150°C) have been recorded and the fundamental vibrations of the axial conformer and several of those for the equatorial form have been assigned. Utilizing two pairs of fundamentals for the two conformers in the krypton solution, an enthalpy difference of 145±15 cm–1 (1.73±0.18 kJ-mol–1) has been obtained with the axial conformer the more stable form. It is estimated that there is 67±2% of the axial conformer present at ambient temperature. Convincing spectroscopic evidence shows that a significant percentage of the chlorocyclopentane molecules are undergoing pseudorotation at ambient temperature. The conformational stabilities, harmonic force constants, fundamental frequencies, infrared intensities, and Raman activities have been obtained from MP2/6-31G(d) calculations with full electron correlation and these quantities have been compared to the experimental values when appropriate. The optimized geometries and conformational stabilities have also been obtained from ab initio MP2 calculations as well as by density functional theory (DFT) by the B3LYP method with several different basis sets. The adjusted r
0 structural parameters have been obtained for both conformers by combining the ab initio data with the previously reported microwave rotational constants. These new values of the structural parameters for both conformers are compared to those previously reported from electron diffraction and microwave studies. These results are compared to the corresponding quantities of some similar molecules. 相似文献
43.
The Raman band contour of the v7 (E') fundamental of PF5 in the gas phase was recorded with a spectral slitwidth of 1.5 cm?1 Failure to observe excited state transitions under this resolution leads to a lower limit for the barrier to Berry pseudorotation of 5.7 kcal mole?1. The experimental contour was compared with a computer generated contour which gave a Coriolis constant, 0.00 ≧ XXX7 ≧ ?0.30, consistent with the calculated value from the sum rule. 相似文献
44.
Gamil A. Guirgis Stephen Bell James R. Durig 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1996,52(14):1861-1873
The infrared (3500-80 cm−1) and Raman (3500-20 cm−1) spectra of 3-fluoro-1-butyne, CH3CHFCCH, have been recorded for the gas and solid. Additionally, the Raman spectrum of the liquid has also been recorded to aid in the vibrational assignment. Ab initio electronic structure calculations of energies, geometrical structures, vibrational frequencies, infrared intensities, Raman activities and the potential energy function for the methyl torsion have been calculated to assist in the interpretation of the spectra. The fundamental torsional mode is observed at 251 cm−1 with a series of sequence peaks falling to lower frequency. The three-fold methyl torsional barrier is calculated to be 1441 ± 20 cm−1 (4.12 ± 0.06 kcal mol−1) where the uncertainty is partly due to the uncertainty in values of the V6 term. A complete vibrational assignment is proposed based on band contours, relative intensities, and ab initio predicted frequencies. Several fundamentals are significantly shifted in the condensed phases compared to values in the vapor state. 相似文献
45.
The Raman (3200 to 10 cm–1) and far infrared (380 to 60 cm–1) spectra of gaseous fluorocyclobutane,c-C4H7F, have been recorded. A series of Q-branches observed in both of these spectra beginning at 166 cm–1 with successive transitions falling to lower frequencies have been assigned to the ring puckering vibrations of both the low energy equatorial and high energy axial conformers. These data have been fit to an asymmetric potential function of the form:V (cm–1)=(1.76±0.05)103X+(4.88±0.28)104X2+(2.12 ±0.16)103 exp(–5.66±0.41)10X2 with a reduced mass function ofg
44= 0.00386–0.00295X+0.03485X2+0.1228X3 +0.3459X4, whereX is the ring puckering coordinate. Utilizing this potential, the difference between the puckering angles for the two conformers was calculated to be 4° with the equatorial conformer having the larger value of 28°. This potential function is consistent with an energy difference between the equatorial and axial forms of 447 cm–1 (1.28 kcal/mol) and a barrier to ring inversion from the equatorial to the axial conformation of 713 cm–1 (2.04 kcal/mol). Experimental values for the enthalpy difference between the two conformers have been determined for both the liquid (400±30 c–1) and gas (413±43 cm–1) from investigations of the Raman spectra at variable temperatures. The conformational stability, enthalpy difference, structural parameters, and fundamental vibrational frequencies, which have been determined experimentally, are compared to those obtained from ab initio Hartree-Fock calculations employing the 3-21G, 6-31 G*, and 6-31 G** basis sets.For part LVIII, seeStruct. Chem.
1991,2, 195.Taken in part from the thesis of M. J. Lee, which has been submitted to the Department of Chemistry in partial fulfillment of the Ph.D. degree, May 1991. 相似文献
46.
47.
The microwave spectra of tertiarybutylphosphine (CH3)3CPH2, (CH3)3CPHD, and (CH3)3CPD2 have been recorded in the region 26.5–40.3 GHz. Both a- and c-type transitions were observed and assigned for the “light” and “heavy” molecules and a-type transitions were observed and assigned for the d1 species. The rigid rotor rotational constants were determined to be A = 4397.63 ± 0.04, B = 2878.88 ± 0.02, and C = 2870.86 ± 0.02 MHz for (CH3)3CPH2 and A= 4261.98 ± 0.04, B = 2769.82 ± 0.02, and C = 2752.71 ± 0.02 MHz for (CH3)3CPD2 and A = 4330 ± 2, B = 2831.45 ± 0.02, and C = 2801.50 ± 0.02 MHz for (CH3)3CPHD. Dipole moment components of |μa| = 1.06 ± 0.02, |μc| = 0.49 ± 0.02 and |μt| = 1.17 ± 0.02D were determined from the Stark effect. By assuming reasonable structural parameters for the tertiarybutyl and phosphine groups, a least-squares fit of the rotational constants gave and . No splitting was observed of the first excited state of the phosphine torsional mode. 相似文献
48.
The microwave spectra of six isotopic species of methylchloroformate, ClCO2CH3, have been recorded from 18.0 to 40.0 GHz. Structural parameters have been determined, and it is shown that the only stable conformer at ambient temperature is the s-trans. The Raman and far infrared spectra of the vapor are reported. Four cases of Fermi resonance have been observed in the Raman effect. Both the methyl and methoxy torsions have been observed in the far infrared, and the methyl barrier to internal rotation has been determined to be 1.15 kcal/mole (1.19 kcal/mole for the CD3 rotor), which is in agreement with the 1.23 kcal/mole obtained from the microwave splitting method. It is shown from both the 13C and 1H NMR spectra along with the far-infrared data that only one conformer exists, which is contrary to what was previously reported. The vibrational spectrum of the solid is also reported and discussed. 相似文献
49.
Variable temperature studies of the infrared spectra (3500–400 cm−1) of 1-pentyne, CH3CH2CH2CCH, dissolved in liquid xenon (−55 to −100°C) and liquid krypton (−105 to −150°C) have been recorded. These data indicate that the anti (methyl group trans to the acetylenic group) and gauche conformers have relative concentrations that vary with the temperature, i.e. enthalpy nonzero. Utilizing seven sets of conformer pairs for the xenon solution and ten sets of conformer pairs for the krypton solution, the enthalpy difference has been determined to be 50±6 cm−1 (0.60±0.07 kJ/mol) and 45±4 cm−1 (0.54±0.05 kJ/mol), respectively, with the anti conformer the more stable form. Because of two equivalent gauche forms, this conformer is estimated to be in higher abundance at 61±1% in the xenon solution and 62±1% in the krypton solution. Optimized geometries and conformational stabilities have been obtained from ab initio calculations with basis sets 6-31G(d), 6-311+G(d,p), 6-311+G(2d,2p) and 6-311+G(2df,2pd) with full electron correlation by the perturbation method to second order (MP2). All of the calculations predict the gauche rotamer to be the more stable form with a high value of 181 cm−1 from the MP2/6-311+G(d,p) calculations and a low value of 107 cm−1 from the MP2/6-311+G(2d,2p) calculation. The ro adjusted structural parameters have been obtained from a combination of the microwave rotational constants and ab initio predicted parameters. The values are compared to the recently reported values from an electron diffraction study where the value for the CC bond distance appears to be too long. The results are discussed and the conformational stability is compared to those obtained for some similar molecules. 相似文献
50.
A. A. S. El Khaldy J. R. Durig 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):227-236
Abstract Mixed chloride dialkyl and alkylenedithiophosphates of ruthenium (III). RuC13-n|(S2P(OR)2|n (R = Prn, and Ph) and RuCl3-n,[S2 POGO]n G =-CMe2CMe2,- CH2CMe2CH2-, -CH2CEt2CH2-. and -CMe2CH2CHMe-, n = 1,2 have been synthesized for the first time by the reactions of ruthenium trichloride with ammonium dialkyl and alkylenedithiophosphate or alternatively by disproportionation reactions of ruthenium trichloride with ruthenium tris(dialkyl and alkylenedithiophosphates) in different stoichiometric ratios in benzene. These new complexes have been characterized by elemental analysis, molecular weight determinations, as well as IR and NMR (1H and 31P) data. Chelated structures with bidentate dialkyl and alkylenedithiophosphates groups have been proposed for all these derivatives. 相似文献