15min:

NATHAN A. SEIFERT, SIMON LOBSIGER, BROOKS H. PATE, Department of Chemistry, University of Virginia, McCormick Rd., Charlottesville, VA 22904-4319; GAMIL A. GUIRGIS, JASON S. OVERBY, Department of Chemistry & Biochemistry, College of Charleston, Charleston, SC 29424 USA; JAMES R. DURIG, Department of Chemistry, University of Missouri-Kansas City, Kansas City, MO 64110 USA.

The structures of CH₃SiHF-NCO, 1-X-silacyclopropane (X = cyano, isocyanato), 1,1,3,3-tetrafluoro-1,3-disilacyclopentane and its hydrogen analogue (1,3-disilacyclopentane), and 1-isocyanato-silacyclohexane have been studied by chirped pulse FTMW spectroscopy in the 6-18 GHz band. Multiple conformers for some of the species were also detected: anti and gauche for both silacyclopropyl species, and axial and equatorial for the silacyclohexane. Heavy atom substitution structures were determined, with all possible single ¹³C, ²⁹Si/³⁰Si and most ¹⁵N isotopologues assigned in natural abundance. Nitrogen hyperfine and distortion parameters for all species have been determined, and the barrier for methyl internal rotation for CH₃SiHF-NCO has been determined as 481(20) cm^-1, close to the B3LYP/6-311++g(d,p) barrier of 450 cm^-1. A summary of the microwave and structural results for the aforementioned molecules will be presented. In addition, emphasis will be placed on the use of previously discussed automated fitting techniques as a means of efficient and fast assignment of isotopologues in spectra with increasingly large line densities.