THE FAR INFRARED SPECTRA OF 1,3-DIOXOLANE AND TETRAHYDROFURAN
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Date
1966
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Ohio State University
Abstract
The phenomenon of pseudorotation in a five membered ring molecule produces a characteristic far infrared spectrum such as that of $tetrahydrofuran.^{1}$ The spectrum consists of two parts. The first is a series of equally spaced peaks superimposed upon a strong continuum below $100 cm^{-1}$ corresponding to $\Delta n = \pm 1$ transitions between pseudorotational energy levels. The second part of the spectrum is a very broad single peak with much fine structure between 200 and $300 cm^{-1}$ corresponding to the $v = 0\rightarrow 1$ transition of the radial vibration in combination with $\Delta n = \pm 1$ pseudorotational transitions. It has now been found that 1,3-dioxolane has a far infrared spectrum very similar to that of tetrahydrofuran and, therefore, it too pseudorotates. The fine structure of the single broad peak in the spectra of both compounds was studied under high resolution and found to be very complex. An absorption at $145 cm^{-1}$ has been found for both compounds. This is probably a hot band of the anharmonic radial mode. A barrier to pseudorotation will split the $\pm n$ degeneracy of the pseudorotational levels, with the splitting decreasing with increasing n. The variation of rotational constants with n can result in an additional splitting of the Q-branches into two peaks. It is possible that the observed splitting of the low frequency peaks can be explained as a combination of the two preceding effects.
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This work was supported in part by the National Science Foundation. $^{1}$ W. J. Lafferty, D. W. Robinson, R. V. St. Louis, J. W. Russell and H. L. Strauss. J. Chem. Phys. 42, 2915 (1965).
Author Institution: Department of Chemistry, University of California
Author Institution: Department of Chemistry, University of California