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The incorporation of pulsed-field gradients for coherence selection into 1D proton-detected pulse sequences provides clean spectra free of cancellation artifacts but, frequently, at the expense of a sensitivity loss by a theoretical factor of 2 due to the rejection of another contributed pathway. A series of slightly modified gradient-enhanced 1D carbon-selective HMQC-and HSQC-relayed experiments are proposed to obtain maximum signal-to-noise ratios in the same overall acquisition time. In contrast to the implementation of this so-called PEP approach in multi-dimensional experiments, the proposed 1D experiments do not have extra requirements for data acquisition or data processing with respect to the original ones and the excellent spectral quality due to of gradient-selected experiments is preserved. Copyright  2001 John Wiley & Sons, Ltd. KEYWORDS: NMR; selective experiments; pulsed field gradients; sensitivity improvementUndoubtedly, sensitivity is the major handicap of NMR spectroscopy when used as an analytical tool. Hence the design of new NMR experiments or the improvement of the sensitivity and/or the resolution of already existing NMR pulse sequences is a permanent challenge for the spectroscopist in order to have the benefit of the most valuable methodologies.Nowadays, an extended arsenal of modern 1D and 2D NMR methodologies are suitable for the effective, complete and quick structural characterization of small-and mediumsized molecules. Of these, selective 1D experiments offer optimized selectivity, specific information and, most important, better resolution and reduced acquisition times when compared with equivalent multi-dimensional counterparts.

New spin-state-selective (S3) NMR pulse sequences exclusively applying cross-polarization schemes to achieve optimum homonuclear and heteronuclear 1H-X coherence transfer are reported for the simple and accurate measurement of the magnitude and sign of heteronuclear coupling constants for samples at natural abundance. The proposed spin-edited HCP-TOCSY experiments are based on clean heteronuclear S3 excitation, generated by simultaneous co-addition of two independent in-phase and anti-phase components created during the mixing heteronuclear J-cross-polarization (HCP) step, which is finally transferred to other protons by a conventional homonuclear TOCSY mechanism. Selective 1D and non-selective 2D approaches for the easy determination of long-range proton-carbon and proton-nitrogen coupling constants on any protonated and non-protonated heteronuclei are presented and discussed for several organic molecules.