Resolved Two-Dimensional Spectroscopy

This is perhaps the best known two-dimensional experiment. Its purpose is to turn all spin multiplets through 90°, and thus to disentangle their overlaps. The experiment has obvious value for crowded coupled spectra such as those of silicate oligomers. 

The actual experiment is deceptively similar to SECSY, with the only important difference being that the second 90° pulse is replaced by a 180° one. This latter pulse does not mix the A and X spins, however. It merely inverts each, so that each component of each multiplet simply becomes its partner. Thus where one A spin was 

In this experiment all motion after the first pulse occurs in the xy plane, and the second frequency is detected as a phase modulation of the resulting spin-echo (Section 5.3). 

Suitable scaling produces the desired spectrum, which also has the advantage that the J axis is not affected by inhomogeneity in Bq, so that very accurate coupling constants may be obtained. Once again, however, there is a drawback. Markedly second-order multiplets give unsatisfactory spectra with unwanted extra peaks, and even first-order spectra have nonstandard peak intensity ratios. The method is also prone to artifacts. 

Schneider, W. G. Bernstein, H. J. High-Resolution Nuclear Magnetic Resonance McGraw-Hill New York, 1959 pp. 31 0. 

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Most demonstrations of J-resolved two-dimensional spectroscopy have been heteronuclear, using experiments, and the... 

Fourier transformation of the echo permits one to inspect the time evolution of such individual resonances. Indeed, their evolution may be treated as a new type of FID, and therefore Fourier-transformed in a second dimension. This is the basis of /-resolved two-dimensional spectroscopy, which is described in a more general context in Section 8. 

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