3,3-dimethylcyclopropene:: Theoretical structure, experimental vibrational spectrum and its cab initio analysis

Samples of 3,3-dimethylcyclopropene and 3,3-dimethylcyclopropene-1-d were synthesized by standard methods. The Raman spectra of 3,3-dimethylcyclopropene and 3,3-dimethylcyclopropene-1-d were measured in the liquid phase. Some bands of 3,3-dimethylcyclopropene-1,2-d(2) were also detected in the second sample. The infrared spectrum of 3,3-dimethylcyclopropene was obtained for a crystalline film. Complete geometry optimization and calculations of the quantum mechanical force field were performed at the ab initio HF/6-31G* level. A set of scale factors was compiled from the sets of scale factors for cyclopropene and 1-methyl- and 1,2-dimethylcyclopropenes, and the force field was scaled using the Pulay scaling technique. The vibrational problems were solved, and complete assignments were suggested for the experimental spectra of 3,3-dimethylcyclopropene, 3,3-dimethylcyclopropene-1-d, and 3,3-dimethylcyclopropene-1,2-d2. The assignments were made taking into account potential energy distributions and correlations between experimental band intensities and depolarization ratios and their theoretical values obtained from the unsealed quantum mechanical force field.