Mohammad A. Qtaitat

Conformational analysis and structural determinations from ab initio calculations for vinyl silyl chloride

The structural parameters for both the cis and gauche rotamers of vinyl silyi chloride, CH2CH-SiH2Cl, were calculated using ab initio Hartree-Fock gradient calculations employing the 3-21G∗ and 6-31G∗ basis sets. These results are compared with the r0 values obtained experimentally from previously reported microwave data. Potential-surface calculations were carried out to determine the barriers to internal rotation and the conformational stability of the two retainers. At the 6-31G∗ basis-set level the cis to gauche and gauche to gauche barriers are 442 cm−1 (1.26 kcal mol−1) and 689 cm−1 (1.97 kcal mol−1), respectively, with the gauche conformer more stable than the cis form by 225 cm−1 (643 cal mol−1). The results are compared with the corresponding data for some similar molecules.

Infrared and raman spectra, conformational stability, barriers to internal rotation, ab initio calculations, ro structure, and vibrational assignment for methyl vinyl silane

Abstract The infrared (3250 to 40 cm −1 ) and Raman (3250 to 10 cm −1 ) spectra of gaseous and solid methyl vinyl silane (CH 2 CHSiH 2 CH 3 ) 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 and gauche conformers have been observed at 98.68 and ∼73 cm −1 , 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: V 1 = 56 ± 11, V 2 = 79±6, V 3 = 600 ± 16, V 4 = 31 ± 6, and V 6 = 64 ± 6 cm −1 , with the cis conformer thermodynamically preferred by 124 ± 33 cm −1 (355 ± 94 cal mol −1 ). The cis to gauche , gauche to gauche , and gauche to cis barriers are 696 (1.99 kcal mol −1 ), 532 (1.52 kcal mol −1 ), and 572 cm −1 (1.64 kcal mol −1 ), 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 −1 (726 ± 46 cal mol −1 ) 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.

Spectra and structure of silicon containing compounds. XXII. Raman and infrared spectra, conformational stability, vibrational assignment and ab initio calculations of methylvinyldichlorosilane

Abstract The infrared (3500–40 cm −1 ) and Raman (3500–20 cm −1 ) spectra of gaseous and solid methylvinyldichlorosilane, CH 2 CHSiCl 2 CH 3 , have been recorded. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values obtained. Both the cis and gauche conformers have been identified in the fluid phases but only the cis conformer remains in the solid. Variable temperature (−60 to −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 77 ± 8 cm −1 (220 ± 23 cal mol −1 ), with the cis conformer being the more stable rotamer. A complete vibrational assignment is proposed for the cis conformer based on infrared band contours, relative intensities, depolarization values and group frequencies. Several of the fundamentals for the gauche conformer have also been identified. The vibrational assignments are supported by normal coordinate calculations. Complete equilibrium geometries have been determined for both rotamers by ab initio calculations employing the 3–21G∗ and 6–31G∗ basis sets at the levels of restricted Hartree-Fock (RHF) and Moller-Plesset (MP) to second order. The frequencies for the normal modes and the potential energy terms for the conformer interconversion have been obtained from the RHF 6–31 G ∗ calculation. The results are discussed and compared to those obtained for some similar molecules.

Spectra and structure of silicon containing compounds: XXIII. Raman and infrared spectra, conformational stability, vibrational assignment and ab initio calculations of dimethyl vinyl chlorosilane

Abstract The infrared (3500 to 40 cm −1 ) and Raman (3500 to 20 cm −1 ) spectra of gaseous and solid dimethyl vinyl chlorosilane, CH 2 CHSi(CH 3 ) 2 Cl, have been recorded. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values obtained. Both the cis and gauche conformers have been identified in the fluid phases but only the gauche conformer remains in the solid. Variable temperature (− 60 to − 100°C) studies of the infrared spectra of dimethyl vinyl chlorosilane dissolved in liquid xenon have been recorded. From these data the enthalpy difference has been determined to be 41 ± 9 cm −1 (117 ± 26 cal mol −1 ) with the gauche conformer the more stable rotamer. A complete vibrational assignment is proposed for the gauche conformer based on infrared and Raman relative intensities, depolarization values and group frequencies. Several of the fundamentals for the cis conformer have also been identified. The vibrational assignments are supported by normal coordinate calculations. Complete equilibrium geometries have been determined for both rotamers by ab initio calculations employing the 3-21G∗ and 6-31G∗ basis sets at the levels of the restricted Hartree-Fock (RHF) and Moller-Plesset (MP) to second order. The frequencies for the normal modes and the potential energy terms for the conformer interconversion have been calculated at the MP 2 6-31 G ∗ level. The results are discussed and compared to those obtained for some similar molecules.

Conformational stability from variable temperature infrared spectra of krypton solutions of 1,3-dichloropropane

Abstract The infrared spectra (3500–400 cm −1 ) of krypton solutions of 1,3-dichloropropane, ClCH 2 CH 2 CH 2 Cl, at variable temperatures (−105 to −150 °C) have been recorded. Additionally, the far infrared spectra (500–70 cm −1 ) of the gas and solid have been recorded. All of the fundamental vibrations of the C 2 conformer ( gauche–gauche ) and many of those for the C 1 form ( gauche–trans ) have been assigned. By utilizing seven pairs of fundamentals for these two conformers in the krypton solutions, an enthalpy difference of 272±27 cm −1 (3.25±0.32 kJ/mol) has been obtained for the C 2 versus C 1 conformer with the C 2 conformer the more stable form. For the C 2 v conformer ( trans–trans ), the enthalpy difference has been determined to be 383±38 cm −1 (4.58±0.46 kJ/mol). It is estimated that there is 62±2% of the C 2 form, 33±2% of the C 1 form and 5±1% of the C 2 v conformer present at ambient temperature. Equilibrium geometries and total energies of the three stable conformers have been determined from ab initio calculations with full electron correlation by the perturbation method to second order as well as by hybrid density functional theory calculations with the B3LYP method using a number of basis sets. The MP2 calculations predict the C 1 conformer stability to be slightly higher than the experimentally determined value whereas for the C 2 v conformer the energy difference is much larger than the experimental value. The B3LYP calculations predict a better energy difference for both the C 1 and C 2 v conformers than the MP2 values. A complete vibrational assignment is proposed for the C 2 v conformer and many of the fundamentals have been identified for the C 1 and C 2 forms based on the force constants, relative intensities and rotational-vibrational band contours obtained from the predicted equilibrium geometry parameters. The r 0 structural parameters are estimated from ab initio MP2/6-311+G(d,p) calculations and comparisons are made with the parameters obtained by electron diffraction technique. The spectroscopic and theoretical results are compared to the corresponding properties for some similar molecules.

Spectra and structure of silicon containing compounds of the general formula CH2CHSi(CH3)nCl3−n

Abstract Variable temperature (−60 to −100°C) studies of the infrared spectra of dimethyl vinyl chlorosilane, CH 2 CHSi(CH 3 ) 2 Cl, and methyl vinyl dichlorosilane, CH 2 CHSiCH 3 Cl 2 , dissolved in liquefied xenon have been recorded. For both of these molecules the cis and gauche conformers have been identified in the fluid phases but only the conformer with the methyl group eclipsing the double bond remains in the solid. From these data, the enthalpy difference for dimethyl vinyl chlorosilane has been determined to be 41 ± 9 cm −1 (117 ± 26 cal mol −1 ) with the gauche conformer being the more stable rotamer and, for methyl vinyl silane, the enthalpy difference has been determined to be 77 ± 8 cm −1 (220 ± 23 cal mol −1 ) with the cis conformer being the more stable rotamer. Ab initio calculations have been performed using the MP2/6-31G∗ basis set and a comparison between the calculated skeletal structural parameters for both molecules is made with those obtained for vinyl trichlorosilane as well as with some electron diffraction data.