Abstract
AbstractIn long‐range heteronuclear chemical shift correlation experiments, modulation of the response intensities of cross‐peaks due to other long‐range couplings to the carbon, although slower than that by direct couplings, must be taken into consideration in optimizing the polarization transfer (Δ1) and refocusing (Δ2) delays. The long‐range modulation is experimentally confirmed using the standard CH correlation pulse sequence with a BIRD pulse midway through the refocusing delay. Analysis of aromatic correlations using hypothetical coupling constants shows that, in general, a choice of Δ2 = 0.667Δ1 is better than Δ2 = Δ1 for CCH correlations, particularly when other interfering long‐range couplings are involved. Guidelines for choosing optimal delays are given by response intensity and attenuation factor contours as a function of J and Δ1 values.
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