N.M.R. spectra of theXnAA′ Xn′type

The method described previously for the calculation of the X spectrum for spin systems of of the XnAA′Xn′ type is extended by means of magnetic equivalence factoring to cases in which the long-range coupling constant Jx is non-zero. This coupling is treated as a first-order perturbation to the energy levels obtained when Jx =0, and it is found that Jx may be measured directly from the separations between easily identified lines in the spectrum. A detailed account of the X 3 AA′X 3′ system is given, and the N.M.R. spectrum of fluoro-N,N′-dimethyl-1,3,2,4-diazadiphosphetidine is analysed. The spectral parameters obtained are discussed. A computer programme which calculates the spectra of systems involving magnetic equivalence is used to examine the validity of the approximations in the method.