The conformers of bromomethyl dimethyl chlorosilane studied by vibrational spectroscopy and ab initio methods (original) (raw)
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Journal of Molecular Structure, 2001
Chloromethyl methyl dichlorosilane (ClCH 2 CH 3 SiCl 2 ) was synthesized and the infrared spectra of its vapour, and of the amorphous and crystalline states, cooled to the temperature of liquid nitrogen were recorded. Additional mid IR spectra of the compound, isolated in both argon and nitrogen matrices, were taken at 5 K. Raman spectra of the liquid were recorded in a capillary at various temperatures between 298 and 223 K. The crystal was also studied in a capillary at 210 K and deposited onto a copper ®nger cooled with liquid nitrogen.
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. ᭧
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 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.
Vibrational Spectroscopy
Raman spectra of cyclopropylmethyl dichlorosilane (c-C 3 H 5 )SiCl 2 CH 3 as a liquid were recorded at 293 K and polarization data were obtained. Additional Raman spectra were recorded at various temperatures between 293 and 163 K, and intensity changes of certain bands with temperature were detected. No crystallization was ever obtained in the Raman cryostat in spite of extensive annealing. The infrared spectra have been studied as a vapour, as an amorphous solid at 78 K and as a liquid in the range 600-100 cm −1 . No infrared bands present in the vapour or liquid seemed to vanish upon cooling, and the sample never formed crystals on the CsI window of an infrared cryostat.
Journal of Molecular Structure, 1999
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. ᭧
Infrared and Raman spectra, ab initio calculations and conformational studies of ethyl iodosilane
Journal of Molecular Structure, 2003
Chloromethyl methyl dichlorosilane (ClCH 2 CH 3 SiCl 2 ) was synthesized and the infrared spectra of its vapour, and of the amorphous and crystalline states, cooled to the temperature of liquid nitrogen were recorded. Additional mid IR spectra of the compound, isolated in both argon and nitrogen matrices, were taken at 5 K. Raman spectra of the liquid were recorded in a capillary at various temperatures between 298 and 223 K. The crystal was also studied in a capillary at 210 K and deposited onto a copper ®nger cooled with liquid nitrogen.
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 Raman Spectroscopy, 2001
The infrared spectra of dichloromethylmethyldichlorosilane (Cl 2 CHCH 3 SiCl 2 ) were recorded in the vapour, amorphous and partly crystalline phases and when isolated in argon, nitrogen and krypton matrices at 5 K. Raman spectra of the liquid were recorded at various temperatures between 295 and 147 K. Spectra of the amorphous and annealed crystal deposited on a copper finger at 80 K were obtained. The spectra showed the existence of two conformers, anti and gauche, in the vapour and in the liquid. Approximately 12 infrared bands were reduced in intensity, and six of the same bands present in the fluid phases in the Raman spectra vanished upon crystallization. From the intensity variations of two band pairs with temperature, a 1H • value of 0.4 ± 0.3 kJ mol −1 between the conformers was obtained in the liquid, anti being the low-energy conformer. Small increases and decreases in the IR band intensities were observed in the matrix spectra after annealing to 32 K (nitrogen), 36 K (argon) and 50 K (krypton). The enthalpy difference between the conformers is low in the matrices, but the anti conformer had lower energy than the gauche conformer. Ab initio calculations were performed at the HF/6-311G * level and gave optimized geometries, vibrational wavenumbers and infrared and Raman intensities for the anti and gauche conformers. The conformational energy derived was 4.4 kJ mol −1 with anti being the low-energy conformer. The dipole moments were calculated to be 1.2 and 3.1 D for the anti and gauche conformers, respectively. Correlation between the observed and calculated wavenumbers of both conformers revealed that anti was present in the crystal, and complete assignments of the spectra were carried out.