INFRARED AND RAMAN-SPECTRA, CONFORMATIONAL STABILITY, BARRIERS TO INTERNAL-ROTATION, NORMAL-COORDINATE CALCULATIONS, AND VIBRATIONAL ASSIGNMENT FOR VINYLSILYL CHLORIDE

The infrared (3250-40 cm-1) and Raman (3250-10 cm-1) spectra of the gaseous and solid states of vinylsilyl chloride (CH2CHSiH2Cl) have been recorded. 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 101.9 and 74.8 cm-1, respectively, with each having several upper state transitions. From these transitions, the potential function to internal rotation has been determined with the following values: V1 = 10 +/- 7, V2 = 160 +/- 8, V3 = 606 +/- 4, and V6 = -33 +/- 2 cm-1, with the cis conformer thermodynamically preferred by 124 +/- 19 cm-1 (354 +/- 54 cal/mol). The cis to gauche, gauche to gauche, and gauche to cis barriers are 731 (2.09 kcal/mol), 492 (1.41 kcal/mol), and 607 cm-1 (1.74 kcal/mol), respectively. A variable-temperature study of the liquid was carried out and the enthalpy difference between the two conformers was found to be 98 +/- 11 cm-1 (280 +/- 31 cal/mol) with the cis form being more stable. The data are also consistent with the gauche conformer being the only form present in the solid phase. 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. These results are compared with the results of some related molecules.