Knowledge Bank

The $\Delta H$ of isomerization of bicyclopropyl in the liquid and vapor phases was determined from the relative temperature dependence of Raman bands assigned to the gauche and trans isomers. In both phases, the gauche form is more stable, with $\Delta Hliquid=-188\pm 8$ cal/mole, and $\Delta Hvapor=-91\pm 28$ cal/mole, The result for the liquid agrees with previous infrared measurements, but the vapor result conflicts with that derived previously from electron diffraction data. The Raman spectrum of vinylcyclopropane consists of a series of strong bands which persist throughout the solids, liquid, and vapor phases. In the liquid and vapor phases, a second, weaker set of bands is observed, whose intensity relative to that of the first set increases with increasing temperature. Also a third set of bands may be discerned, whose relative intensity decreases with increasing temperature. These observations are consistent with an equilibrium between three types of rotamers. This data and its interpretation will be discussed.""