Spectra and Structure of Small Ring Compounds. XIX. Vibrational Analysis and the Barrier to Pseudorotation of Germylcyclopentane

Journal of Chemical Physics - Tập 52 Số 12 - Trang 6108-6119 - 1970
J. R. Durig1, James N. Willis1
1Department of Chemistry, University of South Carolina, Columbia, South Carolina 29208

Tóm tắt

The infrared spectrum of germylcyclopentane in the gaseous state has been recorded from 4000 to 33 cm−1 and that of 1, 1-dideutero-1-germylcyclopentane has been recorded from 4000 to 250 cm−1. The Raman spectra of the two liquids have been recorded and depolarization values determined. The data rule out the planar configuration for the germylcyclopentane molecule and are shown to be consistent with the twisted C2 molecular structure. The 39 normal modes have been assigned on the basis of their depolarization values, infrared band contours, isotopic shift factors, band intensities, and “group frequencies.” The ring-bending mode was found at 113 cm−1 in the vapor phase of the “light” compound. The ring-twisting mode for the d0 and d2 compounds was found at 273 and 269 cm−1, respectively, in the Raman spectrum. The 113-cm−1 band in the light compound was found to be the first of a series of Q branches running to lower frequency. This series has been interpreted in terms of a relatively high barrier to pseudorotation. From midinfrared sum bands a similar series of transitions were obtained for the pseudorotation of the d2 compound. A potential function of the form V = − (2043 / 2) (1 − cos2θ) − (21 / 2) (1 − cos6θ) was found to fit nine observed far-infrared transitions of the ring-puckering mode. The calculated barrier to pseudorotation was 5.9 ± 0.1 kcal/mole for the “light” compound, and the spectroscopically derived parameter mq02 was found to be 18.7 × 10−40 g·cm2. The barrier in the corresponding d2 compound is estimated to be 6.0 ± 0.3 kcal/mole. The barriers are considerably higher than one might expect from existing theories and data on torsional barriers.

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Journal of Chemical Physics

Tập 52 Số 12

6108-6119

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