PROTON CHEMICAL-SHIFT SPECTRA

Three related methods are explored for obtaining high-resolution proto n spectra without spin-spin splittings, termed ''chemical-shift spectr a.'' They are based on two-dimensional J spectroscopy, where the F-1 d imension is derived by Fourier transformation of spin-echo modulation, The first technique superimposes the J spectrum on its reflection in the F-1 = 0 axis, creating multiplet patterns in the form of a St, And rew's cross. The other two techniques purge certain antiphase product- operator terms, either by dispersal in an inhomogeneous effective radi ofrequency field oriented at the magic angle (54.7 degrees) or by mean s of a z filter. In all three cases, the two-dimensional multiplets ar e separated by means of a symmetry filter and their centers are taken as a measure of the respective chemical shifts. The 400 MHz proton che mical-shift spectrum of 4-androsten-3,17-dione is presented as an illu strative example, Good separation is achieved, even for interpenetrati ng spin multiplets with near degeneracies in their chemical shifts, Co mplications due to strong-coupling effects are discussed. (C) 1997 Aca demic Press.