Long‐range 19 F– 15 N heteronuclear shift correlation: examination of J ‐modulations associated with broad range accordion excitation

The first demonstrated example of 19 F– 15 N long‐range heteronuclear shift correlation spectroscopy at natural abundance is reported. Because of the very large variation in the size of 2 J (N,F) vs 3 J (N,F) long‐range heteronuclear couplings, the utilization of one of the new accordion‐optimized long‐range heteronuclear shift correlations experiments is essential if all possible correlations are to be observed in a single experiment. A modified IMPEACH‐MBC pulse sequence was used in conjunction with an optimization range from 4 to 50 Hz to demonstrate the technique using a mixture of 2‐ and 3‐fluoropyridine, which had 2 J (N,F) and 3 J (N,F) long‐range couplings of −52 and 3.6 Hz, respectively. Because of the size of the 2 J (N,F) long‐range coupling constant, a J ‐modulation of the long‐range correlation response is observed in the spectrum resulting in a ‘doublet’ in F 1 due to amplitude modulation. The size of the ‘doublet’ is shown to be a function of the parameter selection ( t 1max , T max , T min and spectral width in F 1 ). This behavior is similar to F 1 ‘skew’ associated with long‐range correlation responses in ACCORD‐HMBC spectra which has been analyzed in detail previously. Copyright © 2002 John Wiley & Sons, Ltd.