Knowledge Bank

The far-infrared spectra of the five-membered ring 1,3-oxathiolane have been recorded and analyzed. A series of well-defined bands due to the ring-bending (hindered pseudorotation) vibration originate at 110 $cm-1$. These are separated by about 10 $cm-1$ and extend down to 33 $cm-1$. A second series of bands near 314 $cm-1$ arise from the ring-twisting (radial) mode. Sum, difference, and combination bands between the twisting and bending vibrations have also been observed and these provide a definitive assignment for all of the low-lying energy states. The pseudorotational series can be fit using a one-dimensional periodic potential and a barrier to pseudorotation of 500 $cm-1$. However, the two-dimensional potential surface derived for this molecule provides a more complete picture of the conformational energetics. The calculations were aided by the determination of the appropriate kinetic energy expansions for the two out-of-plane ring motions.