Pure shift NMR approach for fast and accurate extraction of heteronuclear couplings

Abstract

The direct and accurate determination of heteronuclear (ⁿJ_HX, X = ¹⁹F, ³¹P) couplings from the one dimensional ¹H-NMR spectrum is severely hampered due to the simultaneous presence of large numbers of ⁿJ_HH. The present study demonstrates the utility of the pure shift NMR approach for spectral simplification, and precise and direct measurement of heteronuclear couplings. As a consequence of refocusing of homonuclear couplings (ⁿJ_HH) by the pure shift NMR, only heteronuclear couplings (ⁿJ_HX) appear as simple multiplets at the resonance position of each chemically non-equivalent proton, enabling their direct measurement from the 1D-¹H spectrum. The experiment is demonstrated on a number of molecules containing either ¹⁹F or ³¹P, where ⁿJ_HF and ⁿJ_HP could be precisely measured in a straightforward manner. The distinct advantage of the experiment is demonstrated on molecules containing more than one fluorine atom, where most of the available NMR experiments fail or have restricted utility.