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

✍ Scribed by David J. Russell; Chad E. Hadden; Gary E. Martin; Krish Krishnamurthy

• Publisher: John Wiley and Sons
• Year: 2002
• Tongue: English
• Weight: 858 KB
• Volume: 40
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.992

✦ Synopsis

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 1 max , 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.