Double-quantum z-filtered NMR spectra and automated analysis by pattern recognition

A simple variation of double-quantum spectroscopy is described where the transfer of double- into single-quantum coherence is carried out by means of 2 pulses with small flip angles via eigenstate populations and zero-quantum coherences. For systems with 4 or more spins, the sensitivity of the new expt. is comparable to or better than that of conventional double-quantum spectroscopy with a single 90 Deg monitoring pulse. The resulting spectra feature simple 2D multiplets that are composed of juxtapositions of antiphase doublets. The inclusion of pathways involving zero-quantum coherences greatly simplifies exptl. procedures but leads to small deviations from pure 2D absorption peak shapes in systems with 3 or more spins. A simple variation of the technique yields a complementary 2D spectrum which is useful for automated anal. by pattern recognition techniques. Algorithms are described that allow one to det. the topol. of the coupling network and the values of the shifts and coupling consts. The likelihood that a postulated topol. is correct may be detd. from the degree of consistency between expected and exptl. remote multiplets in double-quantum spectra. [on SciFinder (R)]