Three related methods are explored for obtaining high-resolufirst elucidated by Aue et al. (1). A two-dimensional proton tion proton spectra without spin-spin splittings, termed ''chemi-J spectrum (2), obtained by Fourier transformation of spin cal-shift spectra.'' They are based on two-dimensional J spectrosechoes, has only spin multiplets in the F 1 dimension, with the copy, where the F 1 dimension is derived by Fourier transformation conventional coupled proton spectrum in the F 2 dimension. of spin-echo modulation. The first technique superimposes the J Consequently the spin multiplets are aligned along 45Π diagspectrum on its reflection in the F 1 Γ
0 axis, creating multiplet onals of the two-dimensional spectrum and a 45Π projection patterns in the form of a St. Andrew's cross. The other two techshould give singlet responses at the chemical-shift frequenniques purge certain antiphase product-operator terms, either by cies with no spin-spin splittings. In practice there are serious dispersal in an inhomogeneous effective radiofrequency field oricomplicating factors arising from the curious ''phase-twist'' ented at the magic angle (54.7Π) or by means of a z filter. In all lineshape (3) observed in this kind of spectrum, and the 45Π three cases, the two-dimensional multiplets are separated by means of a symmetry filter and their centers are taken as a measure projection of a phase-sensitive J spectrum simply vanishes of the respective chemical shifts. The 400 MHz proton chemical-(4). Despite the considerable effort expended on this probshift spectrum of 4-androsten-3,17-dione is presented as an illuslem (5-12), a generally applicable solution has proved elutrative example. Good separation is achieved, even for interpenesive. The cases of real interest are those where the conventrating spin multiplets with near degeneracies in their chemical tional high-resolution spectrum contains severely overlapshifts. Complications due to strong-coupling effects are discussed. ping spin multiplets. There are also serious complications α§ 1997 Academic Press occasioned by strong-coupling effects. THREE TYPES OF J SPECTRA