Spectroscopic Determination of the Pseudorotation Barrier in Selenacyclopentane

Abstract

The infrared and Raman spectra of selenacyclopentane have been studied. A series of far‐infrared absorption peaks is interpreted to indicate that the five‐membered ring molecule has a large barrier to pseudorotation. The derived potential function is $\mathrm{V(\phi )}{\mathrm{in\; cm}}^{\text{−1}}\text{\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}(1795.4\hspace{0.17em}/\hspace{0.17em}2)[1\hspace{0.17em}−\hspace{0.17em}}\cos \text{(2φ)]\hspace{0.17em}+\hspace{0.17em}(13.45\hspace{0.17em}/\hspace{0.17em}2)\hspace{0.17em}×\hspace{0.17em}[1\hspace{0.17em}−\hspace{0.17em}}\cos \text{(4φ)]\hspace{0.17em}−\hspace{0.17em}(86.19\hspace{0.17em}/\hspace{0.17em}2)[1\hspace{0.17em}−\hspace{0.17em}}\cos \text{(6φ)]}$ with the pseudorotation constant $\text{B\hspace{0.17em}=\hspace{0.17em}1.55}{\mathrm{cm}}^{\text{−1}}$ . Evidence that the molecule has a twisted ${\mathrm{(c}}_2)$ configuration in its lowest few vibrational states has been obtained.