Vibrational spectra and conformational behavior of dicyclopropylmethane

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.