CONFORMATIONAL STRUCTURES AND TORSIONAL POTENTIALS OF SOME 1,2-DIHALOGENATED-1,1,2,3,3,3-HEXAFLUOROPROPANES, AS OBTAINED BY MOLECULAR MECHANICS CALCULATIONS

A series of three 1,2-diX-1,1,2,3,3,3-hexafluoropropanes, XF2C-XCF-CF3 (X = Cl, Br, I), have been studied by molecular mechanics calculation s (MM). For all three compounds, the torsional potentials obtained sho w three torsional minima. The minima are: anti, gauche+ and gauche-. F or X = Cl (CFP) and Br (BFP), anti is the low-energy conformation, whi le for X = I (IFP), gauche+ is the low-energy conformation. Values for the energy differences and torsional barrier heights between the conf ormations are given, as well as the structural parameters for all conf ormations..Energy differences between the conformations are in the ran ge from 0.1 to 1.7 kcal mol-1. Values for the torsional barrier height s lie between 2.4 and 7.5 kcal mol Torsional force constants are calcu lated for all conformations. Values are in the range from 0. 1 15 to 0 . 140 mdyn angstrom rad-2.