Nuclear Magnetic Resonance Spectroscopy. Conformations and Conformational Equilibration of Bis(trifluoromethyl)tetrachloroethane

The factors which influence conformational populations and barriers to rotation in halogenated ethanes do not yet seem well understood. While the favored form for 1,1,2,2-tetrachIoroethane (1a) has the hydrogens gauche, 1,2-difluorotetrachloroethane (1b) has a slight preference for fluorines trans and 1,2-dimethyltetrachloroethane (1c) has a strong preference for methyls trans. The effect of trifluoromethyl groups has now been determined by investigating the temperature variation of the ^(19)F nmr spectrum of bis(trifluoromethyl)-tetrachloroethane (1d) (obtained from the Pierce Chemical Co.) with the aid of a Varian A-56/60A spectrometer and a V-6040 variable-temperature accessory.