The gradient pulse sequences for measurement of small long-range couplings between heteronuclei ((29)Si-(13)C) in natural abundance reported to date (INEPT-(Si,C)gCOSY and INEPT-(Si,C,Si)HMQC) suffer from significant signal loss when these nuclei ((29)Si, (13)C) are coupled through one-bond couplings to protons. This negative effect can be completely eliminated by using non-gradient versions (INEPT-(Si,C)COSY) or by switching proton decoupling off during gradient pulses (modified INEPT-(Si,C,Si)gHMQC pulse sequence). The beneficial effects of these two approaches on the quality of the spectra are demonstrated here.

Institute of Chemical Process Fundamentals of the ASCR v v i Rozvojová 135 CZ 165 02 Prague 6 Suchdol Czech Republic

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