288-06-2Relevant academic research and scientific papers
Conformational stability, r0 structural parameters, ab initio calculations, and vibrational assignment for silacyclopentane
Guirgis, Gamil A.,El Defrawy, Ahmed M.,Gounev, Todor K.,Soliman, Mamdouh S.,Durig, James R.
, p. 73 - 83 (2007)
The infrared spectra (3500-50 cm-1) of the gas and solid and the Raman spectrum (3200-30 cm-1) of liquid silacyclopentane, c-C4H8SiH2, have been recorded. Additionally the infrared spectrum (3200-400 cm-1) of liquid xenon solutions has been recorded at -65 and -95 °C. In all of the physical states only one conformer was detected which is the twisted C2 form. The conformational energetics have been calculated with the M?ller-Plesset perturbation method to the second order, (MP2(full)) as well as with density functional theory by the B3LYP method utilizing a variety of basis sets. All of these calculations predict only one stable conformer i.e. the C2 form with an average barrier to planarity of 2558 cm-1 (30.60 kJ/mol) from the MP2 calculations and a significantly lower value of 1918 cm-1 (22.95 kJ/mol) from the DFT calculations with neither calculations being significantly effect by inclusion of diffuse functions. From the isolated SiH frequency from the SiHD isotopomer the SiH distance was calculated to be 1.486(3) A?. By utilizing the previously reported microwave rotational constants for three isotopomers (28Si,29Si, and 28Si-d2) combined with the structural parameters predicted from the MP2(full)/6-311 + G(d,p) calculations, adjusted r0 structural parameters have been obtained. The determined heavy atom distances are: r0(SiC) = 1.890(5); r0(C2C4) and (C3C5) = 1.547(5); r0(C4C5) = 1. 535(5) A? and the angles in degrees: ∠CSiC = 95.9(5)°; ∠SiCC = 103.3(5)°; ∠CCC = 107.9(5)° with the two dihedral angles ∠SiCCC = -38.3(3)° and ∠CCCC = 52.4(3)°. A complete vibrational assignment is given for the twisted C2 conformer for the normal species and the Si-d2 isotopomer which are supported by normal coordinate calculations utilizing scaled force constants from ab initio MP2(full)/6-31G(d) calculations. The results of these spectroscopic and theoretical studies are discussed and compared to the corresponding results for some similar molecules.
Far-infrared spectra and two-dimensional potential energy surface of silacyclopentane and its deuterated isotopomers
Colegrove, Lloyd F.,Wells, James C.,Laane, J.
, p. 6291 - 6302 (1990)
The far-infrared spectra of silacyclopentane and its 1-d1, and 1,1-d2 isotopomers have been recorded and analyzed.Spectral series corresponding to the bending and twisting transitions were observed.Bend-twist combination bands and bending overtone spectra were also detected.Kinetic energy (reciprocal reduced mass) expansions were calculated for the bending and twisting motions.These were used along with a five-term two-dimensional potencial energy surface in the vibrational Hamiltonian in order to calculate the energy states.The basis sets were carefully generated to ensure that these levels were accurately calculated.The potential energy surface calculation does an excellent job of reproducing the 103 observed transition frequencies.The potential surface has energy minima at twist angles of 30 deg.The barrier to planarity is 2110 +/- 200 cm-1.The bent structure, which corresponds to a saddle point on the surface, has an energy about 1500 cm-1 above the twisted conformation.
