A new method for measuring and assigning long-range 1 H-13 C coupling constants, and the difficulty of deducing which 1 H spin coupling constants is presented. This is based on the HSQC nuclei are coupled to a given 13 C nucleus without extensive pulse sequence with substitution of the 180ะ 1 H pulse by a selective selective decoupling experiments. The second approach is 180ะ 1 H pulse and a 180ะ 13 C pulse in the middle of the evolution to observe the 13 C satellite peaks at natural abundance in the period. The result is an inverse-detected heteronuclear two-dimen-1 H NMR spectra. Difficulties here include the severe overlap sional J-resolved spectrum from which the long-range heteroproblem from resonances from 12 C-containing molecules and nuclear coupling can be determined with reasonable precision and the fact that the required 1 H resonances are often complicated which has the added advantage of allowing the assignment of all by further 1 H-1 H coupling splittings. Methods have more of the long-range coupling constants from the inverted proton to recently been described which allow the measurement of specific heteronuclei. A one-dimensional version of the method is long-range 1 H-13 C coupling constants from the displacealso given which can be represented as a difference spectrum. The approach has been applied to the measurement of three-bond 1 H-ment of two cross peaks in a two-dimensional heteronuclear 13 C couplings from nucleoside base protons to the anomeric carcorrelation spectrum. Again because of the wide spectral bons of the carbohydrate moiety of nucleosides, as these couplings widths and low digital resolution in correlation spectroscopy, are used to determine nucleoside conformations. For the measureand of antiphase lineshape caused by heteronuclear and homent of couplings to quaternary carbons, a modification of the monuclear couplings, it is difficult to obtain precise values pulse sequence for direct heteronuclear detection is presented. The of small coupling constants. Finally, Bax et al. (24,25) have effect of replacing the selective pulse with a hard pulse on alternate developed a new method, called quantitative J correlation, scans is shown to give information useful for assigning spin syswhere long-range coupling constants are derived from intentems, and the performance of the new pulse sequence is assessed sity ratios determined from a comparison of HMBC and a by spectral simulation.