A study of the structure and conformation of 1,1-dicyclopropylethene by gas electron diffraction and ab initio calculations

The molecular structure of 1,1-dicyclopropylethene, c-(C3H5)2CCH2, has been determined by gas electron diffraction (GED) and ab initio calculations. The potential energy surface as a function of the two torsional angles was calculated to examine the conformation of the molecule. The structural model for the GED data analysis was constructed using ab initio calculations at the MP2(full)/aug-cc-pVTZ level of theory. The conformational mixture at about 293 K was determined to be 36(14)% for the trans-gauche form with C1 symmetry and 64(14)% for the gauche-gauche form (mixture of the gauche-gauche form with C2 symmetry (38(27)%) and the gauche-gauche’ form with Cs symmetry (26%)). The uncertainty of the gauche-gauche form with C2 symmetry was estimated by the Hamilton R-factor ratio test. The present result is in agreement with that reported in a previous GED study (Traetteberg et al. J. Mol. Struct. 485–486 (1999) 73). The conformational abundances determined by GED are different from those in liquid xenon determined by a vibrational spectroscopic study (Durig et al., J. Phys. Chem. A. 109 (2005) 1650).

► The molecular structure of 1,1-dicyclopropylethene in the gas phase.
► Studied by gas electron diffraction and ab initio calculations.
► Three-conformational mixture at about 293 K was determined.
► Comparison between the conformation in the gas phase and those in liquid Xe.