Molecular structures and conformational compositions of 1,2-dichloro-1,1,2,3,3,3-hexafluoropropane and 1,2-dibromo-1,1,2,3,3,3-hexafluoropropane, as determined by gas-phase electron diffraction and ab initio calculations

Abstract

The molecular structures and conformational compositions of 1,2-dichloro-1,1,2,3,3,3-hexafluoropropane (CFP) and 1,2-dibromo-1,1,2,3,3,3-hexafluoropropane (BFP) have been studied by gas-phase electron diffraction at 23 and 25°C, respectively. Both compounds form a mixture of two conformers, a more stable anti form (with the C1X bond anti to the C2C3 bond) and a less stable gauche+ form. For CFP and BFP the mole fractions of the anti forms, with uncertainties estimated at 2σ, were found to be 0.67(13) and 0.82(11), respectively, corresponding to energy differences of Δ E CFP = 0.53 and Δ E BFP = 1.0(5) kcal mol −1. To obtain a more detailed investigation of the conformational geometries, results from ab initio molecular orbital calculations have been included in the analysis.