Conformational structures and torsional potentials of some 1,2-dihalogenated-1,1,2,3,3,3-hexafluoropropanes, as obtained by molecular mechanics calculations

Abstract

A series of three 1,2-diX-1,1,2,3,3,3-hexafluoropropanes, XF 2CXCFCF 3 (X = Cl, Br, I), have been studied by molecular mechanics calculations (MM). For all three compounds, the torsional potentials obtained show three torsional minima. The minima are: anti, gauche+ and gauche−. For X = Cl (CFP) and Br (BFP), anti is the low-energy conformation, while for X = I (IFP), gauche+ is the low-energy conformation. Values for the energy differences and torsional barrier heights between the conformations are given, as well as the structural parameters for all conformations. Energy differences between the conformations are in the range from 0.1 to 1.7 kcal mol −1. Values for the torsional barrier heights lie between 2.4 and 7.5 kcal mol −1. Torsional force constants are calculated for all conformations. Values are in the range from 0.115 to 0.140 mdyn Å rad −2.