Double Fourier transformation in high-resolution NMR

Techniques are described for displaying NMR responses as a function of 2 independent frequency parameters, with particular emphasis on the presentation of 13C spectra with the chem. shift information in 1-dimension and the H-13C splittings in the 2nd dimension. The resolving power for these spin multiplets can be significantly better than in conventional NMR, since the linewidths are detd. principally by spin-spin relaxation effects rather than by field inhomogeneity. Modulation is imposed on 13C spin echoes by gating or pulsing the proton-irradn. field, and was analyzed by 2 successive stages of Fourier transformation. A theor. anal., confirmed by expt., indicates that the profiles of the resulting resonances are an admixt. of absorption and dispersion modes in a proportion that changes rapidly as a function of the 2nd frequency parameter. Echoes acquired in the presence of widband proton decoupling lead to a superposition of resonances which (in the case of weak proton-proton coupling) presents an absorption mode profile in both frequency dimensions. [on SciFinder (R)]