NMR spectra of some simple spin systems studied by two-dimensional Fourier transformation of spin echoes

Phase-modulated spin echoes were generated by a 90-180 Deg pulse sequence applied to some strongly coupled proton spin systems (AB, ABX, and ABC), and the modulation was analyzed by 2-dimensional Fourier transformation. Projection of the resulting 2-dimensional spectra onto the F1 axis leads to a J spectrum, whereas projection onto the F2 axis gives the conventional NMR spectrum. Anal. solns. are presented which correctly predict the shape of the AB and ABX J-spectra, and an iterative numerical anal. were used to fit the ABC case. Projections onto the F1-axis are predicted to have exact symmetry about F1 = 0, and this is borne out by expt., whereas the spin multiplets of the conventional high-resoln. spectrum in general lack symmetry. Certain peaks in the 2-dimensional spectra are predicted to have neg. intensities, although no spin population inversion is involved. Exptl. spectra from AB, ABX, and ABC spin systems illustrate these effects, and strong lines of neg. intensity are detected unequivocally. [on SciFinder (R)]