ENERGY-LEVEL ITERATIVE NMR METHOD FOR SETS OF MAGNETICALLY NONEQUIVALENT, CHEMICAL-SHIFT EQUIVALENT NUCLEI

A technique is described which greatly facilitates the use of the Swalen and Reilly energy-level NMR spectral analysis method for spin systems having sets of magnetically nonequivalent, chemical-shift equivalent nuclei and systems in which it is not possible to assign sufficient transitions to link all energy levels within a particular symmetry group of energy levels. As a test of this scheme, results are described for five iterative analyses of the fluorine-19 spectrum of hexafluoro-1,3-butadiene for the cases where the problem is arbitrarily broken into 27, 16, 8, and 4 groups and the actual problem which involves two groups of energy levels. For the 27-group case it is demonstrated that an excellent set of NMR parameters could be derived based on iteration with only 37 experimental lines to determine the 64 energy levels. The problem of convergence in the cases involving many groups of energy levels is discussed.