Investigation of complex networks of spin-spin coupling by two-dimensional NMR

Proton-proton couplings in a sample of 9-hydroxytricyclodecan-2,Sdione were studied by the two-dimensional Fourier transform method proposed by Jeener. Vari-ous techniques were tested for reshaping the two-dimensional responses to remove the long dispersion-mode tails, and to emphasize cross-peaks at the expense of diagonal peaks. Operation with a mixing pulse of relatively small flip angle allows relative signs of coupling constants to be determined by inspection of the two-dimen-sional spectrum. Weak long-range couplings, normally hidden within the linewidth, may be detected, although their magnitudes can only be estimated very approximately. A simple modification of the pulse sequence permits broadband decoupling in one frequency dimension, giving proton spectra without any J splittings