THE FAR-INFRARED SPECTRA AND PSEUDOROTATION OF TETRAHYDROFURAN AND 1,3-DIOXOLANE
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Date
1968
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Ohio State University
Abstract
The phenomenon of pseudorotation of a five-membered ring molecule produces the characteristic far-infrared spectrum which has been reported for $tetrahydrofuran.^{1}$ The series of tetrahydrofuran absorption peaks in the region below $100 cm^{-1}$ was assigned to pseudorotation transitions in which the quantum number changes by one. Because some details of this original assignment were unclear, the far-infrared spectrum of tetrahydrofuran was reexamined. A related compound, 1,3-dioxolane, was also studied and found to pseudorotate, producing a far-infrared spectrum similar to that of tetrahydrofuran. Overtones, in which the pseudorotation quantum number changes by two, were discovered in the $100-200 cm^{-1}$ region of both spectra. With these overtones it is possible to make a consistent assignment of the observed absorption peaks. Although the spectra do not yield detailed information about the expected barriers to pseudorotation, upper limits of about $50 cm^{-1}$ can be set on the barrier heights. The difficulty with the original assignment of tetrahydrofuran was resolved with the discovery that Coriolis interaction terms in the Hamiltonian cause splitting of some of the Q branches in the spectral region below $100 cm^{-1}$.
Description
$^{1}$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