Gamil A. Guirgis

Spectra and Structure of Silicon-Containing Compounds. XXV. Raman and Infrared Spectra, r0 Structural Parameters, Vibrational Assignment, and Ab Initio Calculations of Ethyl Chlorosilane-Si-d2

The infrared (3200 to 400 cm−1) spectra of gaseous and solid and Raman (3200 to 20 cm−1) spectra of liquid and solid ethyl chlorosilane-Si-d2, CH3CH2SiD2Cl, have been recorded. Both the gauche and trans conformers have been identified in the fluid phases, but only the gauche conformer remains in the solid phase. Variable temperature (−105 to −150°C) studies of the infrared spectra of CH3CH2SiH2Cl dissolved in liquid krypton have been carried out. From these data, the enthalpy difference has been determined to be 78±11 cm−1 (0.93±0.13 kJ/mol), with the gauche conformer the more stable form. Utilizing the frequencies of the silicon-hydrogen stretches, from the chlorosilane-Si-d isotopomer, Si—H bond distances of 1.481 and 1.480 Å have been obtained for the gauche conformer and 1.481 Å for the trans conformer. Complete vibrational assignments are proposed for both isotopomers which are consistent with the predicted frequencies utilizing the force constants from ab initio MP2/6-31G(d) calculations. Both the infrared intensities and 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 6-31(d), 6-311++G(d,p), and 6-311+G(2d,2p) basis sets with full electron correlation by the Moller–Plesset (MP) perturbation method to second order. Continuing the previously reported rotational constants from five different isotopomers and the ab initio predicted structural parameters, adjusted r0 parameters have been calculated, which are compared to the corresponding rs parameters. The results are discussed and the theoretical values are compared to the experimental values when appropriate.

Conformational and Structural Studies of 1-Fluoropropane from Temperature Dependant FT-IR Spectra of Rare Gas Solutions and Ab Initio Calculations

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.

Spectra and Structures of Silicon-Containing Compounds. XXIV.* Raman and Infrared Spectra, r0 Structural Parameters, Vibrational Assignment, Barriers to Internal Rotation, and Ab Initio Calculations of Ethylsilane

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 r0 parameters have been calculated and are compared to the corresponding rs 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.

CONFORMATIONAL STABILITY AND VIBRATIONAL ASSIGNMENT OF PROPANAL

Abstract Variable temperature (−52 to −100°C) studies of the infrared spectra (3500–400 cm −1 ) of propanal, CH 3 CH 2 CHO, dissolved in liquid xenon have been recorded and bands due to both the cis and gauche conformers have been identified. From these data, the enthalpy difference has been determined to be 370±21 cm −1 (4.43±0.25 kJ mol −1 ) with the cis conformer (methyl group eclipsing the oxygen atom) the more stable form. Utilizing the new infrared data from the xenon solution, along with some additional Raman data, and ab initio predictions from MP2/6-31G* calculations, several reassignments of the fundamentals have been made for the cis conformer. Additionally, several bands which have been identified as arising from the gauche conformer have also been assigned. Infrared (3500–80 cm −1 ) and Raman (3500–30 cm −1 ) spectra of gaseous, liquid and/or solid CD 3 CD 2 CHO are also reported and the fundamentals assigned for the cis conformer. The spectroscopic and theoretical results are compared to the corresponding quantities for some similar molecules.

Infrared and Raman spectra, conformational stability, barriers to internal rotation, normal-coordinate calculations and vibrational assignments for vinyl silyl bromide

The infrared (3200-30 cm(-1) spectra of gaseous and solid, the Raman spectra (3200-30 cm(-1)) of the liquid and solid vinyl silyl bromide, CH2CHSiH2Br, have been recorded. Additionally, quantitative depolarization values have been obtained. Both the gauche and cis conformers have been identified in the fluid phases but only the gauche conformer remains in the solid. Variable temperature studies from 0 to -87 degrees C of the Raman spectrum of the liquid was carried out. From these data, the enthalpy difference has been determined to be 22 +/- 6 cm(-1) (0.26 +/- 0.08 kJ/mol), with the gauche conformer being the more stable form. The predictions from the ab initio calculations up to MP2/6-311 + + G(2d,2p) basis set favor the gauche as the more stable form. A complete vibrational assignment is proposed for both the gauche and cis conformers based on infrared band contours, relative intensities, depolarization values and group frequencies. The vibrational assignments are supported by normal coordinate calculations utilizing the force constants from ab initio MP2/6-31G(d) calculations and the potential energy terms for the conformer interconversion have been obtained from the same calculations. Complete equilibrium geometries have been determined for both rotamers by ab initio calculations employing a variety of basis sets up to 6-311 + + G(2d,2p) at 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.

Infrared and Raman spectra and ab initio calculations for 2-pentyne

Abstract The infrared spectra (3500–50 cm −1 ) of the gas and solid and the Raman spectrum (3500–30 cm −1 ) of solid 2-pentyne, CH 3 CH 2 CCCH 3 , have been recorded. Additionally, the infrared spectrum (3500–400 cm −1 ) of a xenon solution has been recorded. A complete vibrational assignment is proposed based on infrared band contours, relative intensities, depolarization values, and group frequencies. The assignment is supported by normal coordinate calculations utilizing ab initio force constants. The internal rotational barrier for the CH 3 rotor of the ethyl group was determined to be 1285 cm −1 from the torsional transitions whereas that for the CH 3 rotor attached to the carbon of the triple bond has nearly free rotation. Complete equilibrium geometries have been determined employing several basis sets at the levels of restricted Hartree–Fock (HF), and/or with full electron correlation by the perturbation method to second order (MP2) as well as with a hybrid density functional theory (B3LYP). The results are discussed and compared to those obtained for some similar molecules.

Raman and infrared spectra, conformational stability, ab initio calculations and vibrational assignments for chloromethyl methyl silane

Abstract The infrared (3500 to 30 cm −1 ) spectra of gaseous and solid and the Raman (3500 to 10 cm −1 ) spectra of the liquid with quantitative depolarization ratios and solid chloromethyl methyl silane, ClCH 2 SiH 2 CH 3 , have been recorded. Similar data have also been recorded for the Si-d 2 isotopomer. These data indicate that two conformers are present in the fluid states but only one conformer is present in the annealed crystalline state. The mid-infrared spectra of the sample dissolved in liquified xenon as a function of temperature (− 100 to − 70°C) have been recorded. Utilizing conformer pairs at 738 ( gauche ), 685 ( gauche ), and 700 ( trans ) cm −1 the enthalpy difference has been determined to be 180 ± 18 cm −1 (515 ± 51 cal mol −1 ) with the gauche conformer the more stable species. However, in the spectrum of the solid, the trans conformer is the stable rotamer remaining after the sample is well annealed. Utilizing the SiH stretching frequencies from the infrared spectrum of the ClCH 2 SiHDCH 3 isotopomer, the two SiH bond distances are calculated to be 1.482 and 1.487 A for the gauche conformer. The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios, and vibrational frequencies are reported for both conformers from RHF 6-31 G ∗ and/or MP 2 6-31 G ∗ ab initio calculations. The gauche conformer is predicted to be the more stable rotamer from both ab initio calculations in agreement with the experimental results. The other calculated quantities are compared to the experimentally determined values where applicable as well as with some corresponding results for some similar 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.

Raman and infrared spectra, conformational stability, barriers to internal rotation, and ab initio calculations of bromocarbonyl isocyanate

Abstract The Raman (3100-10 cm−1) and infrared (3100-30 cm− spectra of Bromocarbonyl isocyanate, BrC(O)NCO, have been recorded for the fluid and solid phases. The observed bands are assigned on the basis of the trans conformer (isocyanate group trans to the carbonyl bond) being more stable and the cis conformer being less stable in the fluid phases, and only the trans conformer being present in the solid. Variable temperature studies of the Raman spectrum of the liquid give a ΔH value of 423 ± 42 cm−1 (1.21 ± 0.12 kcal mol−1). A complete vibrational assignment is proposed for the trans conformer, based on infrared band contours, group frequencies, relative intensities, and normal coordinate calculations. Additionally, several fundamentals of the cis conformer have been assigned. The experimental conformational stability and fundamental vibrational frequencies are compared with those obtained from ab initio gradient calculations employing the RHF STO -3 G ∗ basis set and with the corresponding quantities obtained for similar molecules.

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

The infrared (3200-30 cm(-1) spectra of gaseous and solid and the Raman spectra of liquid (3200-30 cm(-1), with quantitative depolarization values, and solid vinyldichlorosilane, CH2=CHSiHCl2, have been recorded. Both the gauche and the cis conformers have been identified in the fluid phases. Variable temperature (105-150 degrees C) studies of the infrared spectra of the sample dissolved in liquid krypton have been carried out. From these data the enthalpy difference has been determined to be 20 +/- 5 cm(-1) (235 +/- 59 J mol(-1) with the gauche conformer the more stable rotamer. It was not possible to obtain a single conformer in the solid even with repeated annealing of the sample. The experimental enthalpy difference is in agreement with the prediction from MP2/6-311 + G(2d,2p) ab initio calculations with full electron correlation. However, when smaller basis sets, i.e. 6-31G(d) and 6-311 + G(d,p) were utilized the cis conformer was predicted to be the more stable form. Complete vibrational assignments are proposed for both conformers based on infrared contours, relative infrared and Raman intensities, depolarization values and group frequencies, which are supported by normal coordinate calculations utilizing the force constants from ab initio MP2/6-31G(d) calculations. From the frequencies of the Si-H stretches, the Si-H bond distance of 1.474 A has been determined for both the gauche and the cis conformers. Complete equilibrium geometries have been determined for both rotamers by ab initio calculations employing the 6-31G(d), 6-311 + G(d,p) and 6-311 + (2d,2p) basis sets at level of Hartree-Fock (RHF) and/or Moller Plesset to the second order (MP2) with full electron correlation. The potential energy terms for the conformer interconversion have been obtained from the MP2/6-31G(d) calculations. The results are discussed and compared with those obtained for some similar molecules.