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Keywords:

  • selHSQMBC;
  • proton–carbon coupling constants;
  • HSQMBC;
  • HMBC;
  • IPAP

The effects of phase modulation due to homonuclear proton–proton coupling constants in HSQMBC-IPAP and HMBC-IPAP experiments are experimentally evaluated. We show that accurate values of small proton–carbon coupling constants, nJCH, can be extracted even for phase-distorted cross-peaks obtained from a selHSQMBC experiment applied simultaneously on two mutually J-coupled protons. On the other hand, an assessment of the reliability of nJCH measurement from distorted cross-peaks obtained in broadband IPAP versions of equivalent HMBC and HSQMBC experiments is also presented. Finally, we show that HMBC-COSY experiments could be an excellent complement to HMBC for the measurement of small nJCH values. Copyright © 2013 John Wiley & Sons, Ltd.