Knowledge Bank

The torsional fundamental of vinyl cyclopropane has been observed in the low-frequency region of the Raman spectrum of a gaseous sample; although strong, the band is broad and no resolvable fine structure is observed. The overtones $(\Delta \nu =2)$ of the torsion are considerably weaker but, as expected, consist of a series of sharp Q-branches beginning at 223 $cm-1$ and progressing toward lower frequency with an average spacing of $4.5cm-1$. Examination of the spectrum in the mid-Raman region has indicated the presence of two rotamers, the most abundant being the s-trans conformer. A study of the temperature dependence of two pairs of bands has yielded a $\Delta H$ of $\sim$ 550 $cm-1$. All of the above data are being used to determine a periodic potential function governing internal rotation in this molecule.