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The infrared spectra (4000–400 cm−1) of gaseous, liquid and solid (cyanomethyl) cyclopropane have been recorded for the first time. Additionally, the Raman spectra (3500–50 cm−1) of condensed phases of this substance have also been obtained. ‘Extra’ Q branches have been observed in the gas-phase infrared spectrum, and six liquid-phase Raman doublets (two of which are also seen in the infrared spectrum of the liquid) have also been observed, wherein one member of each doublet vanishes once the polycrystalline solid state spectrum is obtained. These data have been interpreted in terms of a two conformer (gauche/cis) fluid-phase equilibrium for (cyanomethyl)cyclopropane, with only the gauche conformer remaining in the solid phase. The temperature behavior of the 774/756 and 835/855 cm−1 liquid-phase Raman doublets yields an enthalpy difference between conformers of 0.72±0.10 kcal mol−1, with the gauche conformer the more stable. This ΔH value implies a room-temperature conformational equilibrium for (cyanomethyl)cyclopropane composed of 87% gauche and 13% cis rotamers in the liquid phase. In addition, a vibrational assignment for the 33 normal modes of (cyanomethyl)cyclopropane has been proposed, and it is in excellent agreement with the previously published vibrational assignments for three (halomethyl)cyclopropanes.

Raman spectra of the condensed phases of dicyclopropylmethane have been recorded. In addition, i.r. spectra of this compound have been obtained for all three phases. From the appearance of spectral doublets in the liquid phase Raman (and i.r.) spectra, one member of each of which vanishes upon crystallization, it has been concluded that, in the liquid state, DCPM exists as an equilibrium mixture of at least two conformers. Based upon the spectral results for DCPM, and upon the conformational preferences of a number of related molecules, it has been concluded that these two conformers are the C 2 and C s gauche/gauche rotational isomers, with the C 2 form being the one which remains in the solid phase. From a variable temperature study of liquid phase Raman peaks, it has been determined that the C 2 conformer of DCPM is more stable than the C s conformer by 0.93 ± 0.10 kcal/mole. In addition, it appears that the C 2 rotamer of DCPM also predominates in the gaseous phase. Tentative assignments of the major spectral bands of DCPM have also been proposed.