Raman spectra of gases. VI. Barrier to planarity in germacyclopentane

The anharmonic out‐of‐plane twisting mode of the heavy atom skeleton of germacyclopentane has been observed in the Raman spectrum of the vapor. These data along with the far infrared frequencies for the other out‐of‐plane ring bending mode have made it possible to calculate the two‐dimensional potential surface for these two out‐of‐plane ring modes without any assumptions as to the magnitude of the barrier to planarity. From this two‐dimensional treatment, it is shown that the interconversion between the two twisted configurations is not entirely along the twist axis but the path is actually slightly elliptical and passes through a slightly bent configuration at R₂=0. However, it is shown that the twisting and puckering motions are fairly independent. From the two‐dimensional treatment, one calculates the barrier to interconversion to be $\text{∼ 1450\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ compared to the less accurate value of 2043 cm⁻¹ calculated using the one‐dimensional approximation.