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Long-range CH correlation 2D NMR spectroscopy 3—long-range J modulation of cross-peak intensities

✍ Scribed by V. V. Krishnamurthy; John E. Casida

Publisher
John Wiley and Sons
Year
1988
Tongue
English
Weight
475 KB
Volume
26
Category
Article
ISSN
0749-1581

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✦ Synopsis

In long-range heteronuclear chemical shift correlation experiments, modulation of the response intensities of crosspeaks 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 (A ,) and refocusing (A,) 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 A, = 0.6676, is better than A, = A, for C-CH 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 A, values.

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