Spectra and structure of small ring compounds. LII—Raman and far‐infrared spectra of solid 1,1‐dicyanocyclopropane and ab initio calculations of cyclopropane, cyanocyclopropane and 1,1‐dicyanocyclopropane

The Raman (3500–10 cm−1) and far-infrared (400–70 cm−1) spectra of solid 1,1-dicyanocyclopropane have been recorded. The molecular structure of cyclopropane, cyanocyclopropane and 1,1-dicyanocyclopropane have been calculated by ab initio methods at the 4-31G basis set level. The harmonic force fields for cyanocyclopropane and 1,1-dicyanocyclopropane have also been calculated using the same basis set. By the combination of experimental data and normal coordinate calculations with scaled ab initio force constants, the vibrational assignments for these two molecules have been revised. Discrepancies between the previously reported and present assignments are discussed. The molecular structures of cyanocyclopropane and 1,1-dicyanocyclopropane obtained in this work are compared with the molecular structure of cyclopropane.