Abstract
The microwave spectrum (6500-18 500 MHz) of 1-fluoro-1-silacyclopentane, c-C4H8SiHF has been recorded and 87 transitions for the Si-28, Si-29, Si-30, and C-13 isotopomers have been assigned for a single conformer. Infrared spectra (3050-350 cm(-1)) of the gas and solid and Raman spectrum (3100-40 cm(-1)) of the liquid have also been recorded. The vibrational data indicate the presence of a single conformer with no symmetry which is consistent with the twist form. Ab initio calculations with a variety of basis sets up to MP2(full)/aug-cc-pVTZ predict the envelope-axial and envelope-equatorial conformers to be saddle points with nearly the same energies but much lower energy than the planar conformer. By utilizing the microwave rotational constants for seven isotopomers (Si-28, Si-29, Si-30, and four C-13) combined with the structural parameters predicted from the MP2(full)/6-311+G(d,p) calculations, adjusted r(0) structural parameters have been obtained for the twist conformer. The heavy atom distances in angstrom are: r(0)(SiC2) = 1.875(3); r(0)(SiC3) = 1.872(3); r(0)(C2C4) = 1.549(3); r(0)(C3C5) = 1.547(3); r(0)(C4C5) = 1.542(3); r(0)(SiF) = 1.598(3) and the angles in degrees are: angle CSiC = 96.7(5); angle SiC2C4 = 103.6(5); angle SiC3C5 = 102.9(5); angle C2C4C5 = 108.4(5); angle C3C5C4 = 108.1(5); angle F6Si1C2 = 110.7(5); angle F6Si1C3 = 111.6(5). The heavy atom ring parameters are compared to the corresponding r(s) parameters. Normal coordinate calculations with scaled force constants from MP2(full)/6-31G( d) calculations were carried out to predict the fundamental vibrational frequencies, infrared intensities, Raman activities, depolarization values, and infrared band contours. These experimental and theoretical results are compared to the corresponding quantities of some other five-membered rings. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3673889]