Infrared and Raman Spectra, Conformational Stability, ab Initio Calculations, and Vibrational Assignments for Cyclopropylchlorosilane

Abstract

The infrared (3300−30 cm-1) spectra of gaseous and solid cyclopropylchlorosilane, c-C3H5SiH2Cl, have been recorded. Additionally, the Raman spectra (3200−30 cm-1) of the liquid and solid have been recorded and quantitative 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 (−55 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 98 ± 10 cm-1 (280 ± 29 cal mol-1), but with the cis conformer being the more stable form which is consistent with the predictions from ab initio calculations at the highest level of calculation, MP2/6-311++G**. A complete vibrational assignment is proposed for both the cis and gauche 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* 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** at levels of restricted Hartree−Fock (RHF) and/or Moller−Plesset (MP) to second order. The potential energy terms for the conformer interconversion have been obtained from the MP2/6-31G* calculation. The results are discussed and compared to those obtained for some similar molecules.

Microwave, r0 structural parameters, conformational stability and vibrational assignment of cyclopropylcyanosilane

“…Most of the fundamentals associated with the cyclopropyl ring are expected to have similar frequencies for the two conformers as well as to those previously reported for the corresponding halides, i.e. c-C 3 H 5 SiH 2 Cl [5] and c-C 3 H 5 SiH 2 Br [6]. Hence, the ring modes will not be discussed in detail but instead the emphasis will be on the SiH 2 bends and the CSi(CN) modes.…”

“…However, B3LYP calculations from all the basis sets utilized predicted the gauche conformer as most stable form by an average value of 15 cm À1 (0.18 kJ mol À1 ). For cyclopropyl fluoro, chloro and bromo silanes (c-C3H5SiH2-X; X = F, Cl, Br) the enthalpy difference between the two conformers were determined to be 109 ± 19 cm À1 , 98 ± 13 cm À1 and 126 ± 15 cm À1 with gauche conformer the most stable form for cyclopropylfluorosilane whereas for both cyclopropylchlorosilane and cyclopropylbromosilane cis conformer was observed to be most stable conformer [4][5][6]. For cyanomethylcyclopropane, the enthalpy difference between the cis and the gauche conformer was determined to be 54 ± 4 cm À1 with gauche conformer being the more stable form [39].…”

“…We further investigated cyclopropylfluorosilane [4], cyclopropylchlorosilane [5] and cyclopropylbromosilane [6]. The enthalpy difference was determined to be 109 ± 9 cm À1 (1.30 ± 0.1 kJ/mol) for cyclopropylfluorosilane with the gauche form the most stable conformer, whereas for cyclopropylchlorosilane and cyclopropylbromosilane, the cis conformer was the more stable form with the enthalpy difference of 98 ± 10 cm À1 (1.2 ± 0.12 kJ/mol) and 126 ± 25 cm À1 (1.51 ± 0.30 kJ/mol), respectively, [4][5][6].…”

“…The enthalpy difference was determined to be 109 ± 9 cm À1 (1.30 ± 0.1 kJ/mol) for cyclopropylfluorosilane with the gauche form the most stable conformer, whereas for cyclopropylchlorosilane and cyclopropylbromosilane, the cis conformer was the more stable form with the enthalpy difference of 98 ± 10 cm À1 (1.2 ± 0.12 kJ/mol) and 126 ± 25 cm À1 (1.51 ± 0.30 kJ/mol), respectively, [4][5][6]. It is interesting to note that in cyclopropylchlorosilane and cyclopropylbromosilane both the gauche and cis conformers were present in the liquid phase and only the gauche conformer was present in the solid phase [5,6]. At ambient temperature, 23 ± 2% of cyclopropylfluorosilane was in the cis form, whereas for the cyclopropylbromosilane, the ratio of gauche to cis conformers was almost equal [4,5].…”

“…It is interesting to note that in cyclopropylchlorosilane and cyclopropylbromosilane both the gauche and cis conformers were present in the liquid phase and only the gauche conformer was present in the solid phase [5,6]. At ambient temperature, 23 ± 2% of cyclopropylfluorosilane was in the cis form, whereas for the cyclopropylbromosilane, the ratio of gauche to cis conformers was almost equal [4,5]. For cyclopropylsilane derivatives, conformational stability changes with respect to substitution of halogen in the silane moiety.…”