LIMITATIONS OF THE NMR METHOD TO STUDIES OF ROTATIONAL ISOMERISM.

Author Institution: Division of Pure Chemistry, National Research CouncilNMR and thermodynamic parameters for the two rotational isomers of $CHBr_{2}-CFBr_{2}$ have been obtained from their low temperature $^{1} H$ and $^{19} F$ spectra. The results are in variance with those obtained from the conventional method which utilises the temperature dependence of the time-averaged spectra at higher temperature. Limitations of the second method will be discussed. An analysis of the lineshapes has been made and the barrier to internal rotation has been obtained. The signs of the coupling constants in the two rotamers have been established