Infrared and Raman spectra, ab initio calculations and conformational equilibria of chloromethyl methyl dichlorosilane (original) (raw)
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Journal of Molecular Structure, 2001
The infrared spectra of 1,2-diphenylethane were recorded as a melt and crystalline solid in capillary films and as a pellet in KBr and polyethylene in the 4000-50 cm 21 range. Moreover, the sample was isolated in an argon matrix at ca. 5 K, and the spectra recorded in the range 3100-450 cm 21 , before and after annealing. Raman spectra of the melt were recorded between 295 (supercooled) and 357 K, and spectra of the crystalline solid were obtained at ambient temperature.
The Journal of Physical Chemistry, 1991
The infrared (3250 to 40 cm-') and Raman (3250 to 10 cm-') spectra of gaseous and solid methyl vinyl silane (CH,CHSiH,CHa) have been recorded. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. From the far infrared spectrum of the gas, the fundamental asymmetric torsions for both the cis andgauche conformers have been observed at 98.68 and -73 cm-', respectively, with the cis conformer having several upper state transitions. From these transitions, the potential function to internal rotation has been determined with the following values: VI=56 k 11, V,=79+ 6, V,=SOO k 16, V, = 31& 6, and V, = -64 f 6 cm-', with the cis conformer thermodynamically preferred by 124 ? 33 cm-' (355 ? 94 cal mol-'), The cis to gauche, gauche to gauche, and gauche to cis barriers are 696 (1.99 kcal mol-I), 532 (1.52 kcal mol-'), and 572 cm-' (1.64 kcal mol-'), respectively. A variable temperature study of the Raman spectrum of the liquid was carried out and the enthalpy difference was found to be 254 & 16 cm-' (726 ? 46 cal mol-') with the cis conformer being the more stable form. A complete vibrational assignment is proposed based on infrared band contours, depolarization ratios, and group frequencies. The assignment is supported by an ab initio calculation utilizing the 3-21G* basis set to obtain the force constants and potential energy distribution. Additionally, ab initio calculations have been carried out utilizing the 6-31G* basis set to obtain the conformational stability, barriers to internal rotation and optimized structural parameters. These results are compared with the experimentally determined values as well as to corresponding results of some related molecules.
Journal of Molecular Structure, 2001
The infrared spectra of 2-chloroethyl trifluorosilane (ClCH 2 CH 2 SiF 3 ) were recorded in the vapour, amorphous and crystalline solid phases in the range 4000-50 cm Ϫ1 . Spectra of the compound isolated in argon and nitrogen matrices at 10 K and variable temperature spectra in liquified xenon were obtained. Raman spectra of the liquid were recorded at various temperatures between 298 and 163 K, and the amorphous and crystalline solids studied. The spectra of 2-chloroethyl trifluorosilane showed the existence of two conformers-anti and gauche-present in the vapour and in the liquid. Large variations in the infrared and Raman spectra occurred during the annealing and an intermediate, probably metastable crystal appeared at ca. 125 K with pronounced crystal splitting and apparently containing both conformers. More than 15 infrared and Raman bands present in the fluid phases and in the 125 K crystal vanished in the stable crystal formed at ca. 160 K. From intensity variations with temperature of five Raman band pairs, a DHЊanti-gauche 0:8^0:3 kJ mol Ϫ1 was obtained in the liquid, and in liquid xenon under pressure a DH value of Ϫ0:7^0:1 kJ mol Ϫ1 was obtained from IR spectra. Annealing experiments indicate that the anti conformer has the lower energy in argon and nitrogen matrices as well as in xenon, and the barrier seemed to be ca. 8 kJ mol Ϫ1 . Ab initio calculations were performed using the Gaussian 94 program with the HF/6-311G* basis set and gave optimized geometries, infrared and Raman intensities and scaled vibrational frequencies for the anti and gauche conformers. The conformational energy derived was 3.8 kJ mol Ϫ1 giving anti as the low energy conformer. ᭧
The vibrational spectra and conformers of chloromethyl dimethyl chlorosilane
Journal of Molecular Structure, 1997
The IR spectra of chloromethyl dimethyl chlorosilane were recorded as a vapour and as amorphous and crystalline solids in the 4000-50 cm-' range and isolated in argon and nitrogen matrices at ca. 5 K. Raman spectra were recorded at room temperature and at various temperatures, partly as a super cooled liquid between 295 and 188 K and spectra of the amorphous and crystalline solids were obtained at 80 K and at 185 K.
Journal of Molecular Structure, 2000
Bromomethyl dimethyl chlorosilane (CH 2 Br(CH 3 ) 2 SiCl) was synthesised and the infrared spectra of the vapour and of the amorphous and crystalline states at liquid nitrogen temperature were obtained. Additional spectra of the compound, isolated in argon, nitrogen and xenon matrices were recorded at 5 and 15 K. Raman spectra of the liquid were obtained at various temperatures between 295 and 173 K, and spectra of the amorphous and crystalline solids were recorded.
Journal of Molecular Structure, 1999
Chloromethyl methyldifluorosilane (CH 2 Cl-CH 3 SiF 2) was synthesized for the first time and the infrared spectra were recorded in the vapour, amorphous and crystalline solid phases in the MIR and FIR regions. Additional MIR spectra were obtained for the compound isolated in argon and nitrogen matrices at 15 K. The spectra of chloromethyl methyldifluorosilane showed the existence of two conformers-anti and gauche-present in the vapour and in the liquid. Raman spectra of the liquid were recorded at various temperatures between 298 and 163 K, giving DH (gauche-anti) equal to ca. 0.2 kJ mol Ϫ1. By careful annealing of the amorphous solid formed by depositing the vapour on a cold CsI or silicon window (infrared) or Cu finger (Raman) at 80 K, two different crystals were formed. One of these, obtained after annealing to 150 K, contained the gauche conformer, the other after annealing to ca. 110 K contained molecules in the anti conformer. These experimental data make a very reliable assignment of the conformer bands possible. Ab initio calculations were performed using the gaussian 94 program with the HF/6-311G* basis set and gave optimized geometries, infrared and Raman intensities and scaled vibrational frequencies for the anti and gauche conformers. The conformational energy derived was 5.9 kJ mol Ϫ1 with gauche being the low energy conformer.
Journal of Molecular Structure, 1999
The infrared spectra of gaseous and solid chloromethyl methyl silane, ClCH 2 SiH 2 CH 3 , and chloromethyl methyl difluorosilane, ClCH 2 SiF 2 CH 3 , were recorded. Additionally, the variable temperature infrared spectra of the sample dissolved in liquid krypton and/or xenon were obtained. Both the trans and gauche conformers are present in the fluid phases but only the trans conformer is present in the solid for both molecules. The enthalpy difference between the two conformers for chloromethyl methyl silane was determined to be 180^15 cm Ϫ1 (2.16^0.18 kJ/mol) and for chloromethyl methyl difluorosilane 2361 5 cm Ϫ1 (2.82^0.17 kJ/mol) in xenon with the gauche conformers more stable for both molecules. The enthalpy value for the silane in krypton is 181^18 cm Ϫ1 (2.16^0.09 kJ/mol). Ab initio calculations were carried out at the RHF/6-31G* and MP2/6-31G* levels for both molecules from which structural parameters and conformational stabilities were determined. ᭧
Journal of Molecular Structure, 2001
Infrared spectra of n-propyltrichlorosilane (CH 3 CH 2 CH 2 SiCl 3 ) were obtained in the vapour, amorphous and crystalline solid phases in the range 4000-50 cm −1 . Additional spectra in argon and nitrogen matrices at 5 K were recorded before and after annealing to 20-36 K. Raman spectra of the compound as a liquid were recorded at various temperatures between 300 and 153 K and spectra of the amorphous and crystalline solids were obtained. The spectra revealed the existence of two conformers (anti and gauche) in the fluid phases and in the matrices. When the vapour was shock-frozen on a cold-finger at 78 K and subsequently annealed to 120-130 K, 10 Raman bands and eight IR bands of the liquid were reduced in intensity in the amorphous phase and vanished in the crystal. Frequent intensity variations were observed in the infrared spectra of argon and nitrogen matrices before and after annealing. These spectra revealed the existence of one conformer (anti) in the crystal. From intensity variations of four independent pairs of anti and gauche bands in the Raman spectra between 300 and 150 K, an average value 1H • (gauche-anti) = 4.6 ± 0.3 kJ mol −1 was obtained in the liquid. Annealing experiments on n-propyltrichlorosilane in the matrices demonstrate that the gauche bands vanish after annealing, revealing that the anti conformer has the lower energy. The spectra of both conformers were interpreted in detail. Ab initio and DFT calculations gave optimized geometries, infrared and Raman intensities and scaled vibrational wavenumbers for the anti and gauche conformers. The conformational energy difference derived was 7.6 and 6.4 kJ mol −1 for the HF/6-311G * and B3LYP/6-311G * basis sets, respectively, with anti being the low-energy conformer.
Journal of Molecular Structure, 2002
The infrared (3400-50 cm 21 ) and/or Raman (3400 -10 cm 21 ) spectra of gaseous, xenon solution, liquid and solid 5chloropent-2-yne, CH 2 ClCH 2 CCCH 3 , have been recorded. These data indicate that the molecule exists in the anti (the C -Cl bond is trans to the CxC bond) and the gauche conformations in the vapor and liquid but only the anti conformer remains in the solid state. From a variable temperature infrared study of the xenon solution, the anti conformation has been determined to be more stable than the gauche form by 233^23 cm 21 (2.79^0.28 kJ/mol) and it is estimated that 39% of the sample is in the gauche form at ambient temperature. The optimized geometries, conformation stabilities, harmonic force fields, Raman activities, depolarization ratios, and infrared intensities have been obtained from ab initio MP2/6-31G(d) calculations with full electron correlation. These predicted quantities are compared to the corresponding experimental quantities when appropriate. Equilibrium geometries and energies for both conformers have been obtained from ab initio MP2/6-311G(d,p), MP2/6-311G(2d,2p) and MP2/6-311G(2df,2pd) calculations. Vibrational assignments for the 24 normal modes for the anti conformer are proposed and several of the fundamentals for the gauche conformer are assigned. The sub-band structure on the pseudodegenerate vibrations of the methyl group indicates that it is almost free internal rotation. From this fine structure, the Coriolis coupling constants, j, have been determined. These experimental and theoretical results are compared to the corresponding quantities of some similar molecules. q