Knowledge Bank

Carbon-carbon bond distances in the cyclopropane ring have been predicted co vary significantly with the electronic nature of substituent $groups.1,2$ Substitution structures give $R12=R23=1.514$ {\AA} in cyclopropyl $chloride3$, and $R12=1.464$ and $R23=1.553$ in 1 1-$difluorocyclopropane.4$ The structure of cyclopropyl cyanide is of interest to determine: (1) whether $R23$ is shorter than 1.514 {\AA}, and (2) whether $R12$ and $R23$ are unequal. The spectra of cyclopropyl $cyanide6$, and the 2-substituted $C13$ isotope have been $reported.5$ The spectrum of the 1-substituted $C13$ isotope has been observed in natural abundance by modulated microwave- and radio frequency-microwave double resonance methods and conventional Stark modulated spectroscopy. Rotational constants for the three species in the rigid rotor approximation are, in MHz: $C12:A=15785.821\pm 0.04,B=3465.072\pm 0.006,C=3286.199\pm 0.007;C113:A=15614.90\pm 0.1,B=3454.776\pm 0.008,C=3284.329\pm 0.006;C213:A=15496.471\pm 0.04,B=3421.868\pm 0.006,C=3236.838\pm 0.005$. These results give $R12=1.529\pm 0.01$ {\AA} and $R23=1.500\pm 0.004$ {\AA}. The direction of change in bond length is in accord with Hoffman’s predictions. The structural parameters are being refined to correct for centrifugal $distortion.1$R. Hoffman, Tetrahedron Letters 33, 2907 (1970). $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$R. E. Penn and J. E. Boggs, J. C. S. Chem. Comm. 11, 666 (1972). $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$R. H. Schwendeman, G. D. Jacobs, and T. H. Krigas, J. Chem. Phys. 40, 1022 (1964). $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$A. T. Perretta and V. W. Laurie, presented at the Symposium on Molecular Structure and Spectroscopy, The Ohio State University, June, 1973. $\mathrm{<mrow\; data-mjx-texclass="ORD">5</mrow>}$R. Pearson, JR., and V. W. Laurie, ibid. $\mathrm{<mrow\; data-mjx-texclass="ORD">6</mrow>}$J. P. Friend and B. P. Dailey, J. Chem. Phys. 29, 577 (1958)