Knowledge Bank

Two recent publications have corrected earlier work on cyclopropyl cyanide (CPCN), providing more complete spectra and new assignments for this $molecule.1,2$ As yet, however, no deuterium labelling has been reported for CPCN (or any other monosubstituted cyclopropane) to lend support to these assignments. We have synthesized CPCN-$\alpha -d1$ and recorded its infrared spectra in all phases and Raman spectra for the condensed phases. In addition, we have obtained the solid phase Raman spectrum, and a higher resolution ($0.5cm-1$) gas phase infrared spectrum of the light compound, CPCN. On the basis of Raman depolarization ratios, gas-phase infrared band contours, and isotopic shifts, we have proposed assignments for the vibrational fundamentals of these two molecules. Since the CH in-plane bending mode in CPCN falls $50-60cm-1$ higher than typical for substituted cyclopropanos, and since the CD out-of-plane bend in CPCN-$\alpha -d1$ occurs at an anomalously low frequency, it would appear that the CN group perturbs the electronic structure of the three membered ring, especially in the vicinity of the $C1$ carbon atom. In addition, some large gas-phase to liquid-phase frequency shifts may indicate that self-association occurs in the liquid phase of CPCN.