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 s ynthesized by standard methods. The Raman spectra of 3,3-dimethylcycloprope ne 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 secon d sample. The infrared spectrum of 3,3-dimethylcyclopropene was obtained fo r a crystalline film. Complete geometry optimization and calculations of th e 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 f or cyclopropene and 1-methyl- and 1,2-dimethylcyclopropenes, and the force field was scaled using the Pulay scaling technique. The vibrational problem s 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.