400
Acc. Chem. Res. 1980,13, 400-406
The JMethod: Application of NMR Spectroscopy to the Determination of Small Internal Rotation Barriers in Solution WILLIAMJ. E. PARR Malaysian Rubber Producers Research Association, Brickendonbury, Hertford SG3 BNP, England
TEDSCHAEFER” Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2 Received January 14, 1980
A variety of methods has been employed in the investigation of the number of rotational isomers of a molecule, their relative energies, and the heights of the potential-energy curves for internal rotation. These include thermodynamics (heat capacities), molecular orbital calculations, electron diffraction, microwave and vibrational spectroscopies, relaxation measurements, and NMR spectroscopicstudies. The method of choice’ for any particular molecule depends upon the molecular structure, the magnitude of the barrier to internal rotation, and the approximations of the model to be applied. For barriers of
