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.

The Naval Research Laboratory (NRL) Mobile

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